diff --git a/src/View/BoundaryCondition/Edit/Table.py b/src/View/BoundaryCondition/Edit/Table.py
index 363aa19f..d36f56f5 100644
--- a/src/View/BoundaryCondition/Edit/Table.py
+++ b/src/View/BoundaryCondition/Edit/Table.py
@@ -97,7 +97,9 @@ class TableModel(PamhyrTableModel):
                 if self._opt_data == "time":
                     value = timestamp_to_old_pamhyr_date(int(v))
                 else:
-                    value = str(datetime.fromtimestamp(v))
+                    value = str(
+                        self._start_date + timedelta(seconds=float(v))
+                    )
             else:
                 value = f"{v}"
 
@@ -114,6 +116,10 @@ class TableModel(PamhyrTableModel):
         column = index.column()
 
         try:
+            if (self._data.header[column] == "time"
+                    and self._opt_data == "date"):
+                value = self.date_to_elapsed_seconds(value)
+
             row = self.get_true_data_row(row)
 
             self._undo.push(
diff --git a/src/View/BoundaryCondition/Edit/Window.py b/src/View/BoundaryCondition/Edit/Window.py
index 29281d6f..788b1203 100644
--- a/src/View/BoundaryCondition/Edit/Window.py
+++ b/src/View/BoundaryCondition/Edit/Window.py
@@ -173,7 +173,8 @@ class EditBoundaryConditionWindow(PamhyrWindow):
             },
             data=self._data,
             undo=self._undo_stack,
-            opt_data=self._study.time_system
+            opt_data=self._study.time_system,
+            start_date=self._study.date
         )
 
         table.setModel(self._table)
diff --git a/src/View/BoundaryConditionsAdisTS/Edit/Table.py b/src/View/BoundaryConditionsAdisTS/Edit/Table.py
index eeba2689..01179d92 100644
--- a/src/View/BoundaryConditionsAdisTS/Edit/Table.py
+++ b/src/View/BoundaryConditionsAdisTS/Edit/Table.py
@@ -87,7 +87,9 @@ class TableModel(PamhyrTableModel):
                 if self._opt_data == "time":
                     value = timestamp_to_old_pamhyr_date(int(v))
                 else:
-                    value = str(datetime.fromtimestamp(v))
+                    value = str(
+                        self._start_date + timedelta(seconds=float(v))
+                    )
             else:
                 value = f"{v}"
 
@@ -104,6 +106,10 @@ class TableModel(PamhyrTableModel):
         column = index.column()
 
         try:
+            if (self._data.header[column] == "time"
+                    and self._opt_data == "date"):
+                value = self.date_to_elapsed_seconds(value)
+
             row = self.get_true_data_row(row)
 
             self._undo.push(
diff --git a/src/View/BoundaryConditionsAdisTS/Edit/Window.py b/src/View/BoundaryConditionsAdisTS/Edit/Window.py
index 9ae31212..09670489 100644
--- a/src/View/BoundaryConditionsAdisTS/Edit/Window.py
+++ b/src/View/BoundaryConditionsAdisTS/Edit/Window.py
@@ -120,7 +120,8 @@ class EditBoundaryConditionWindow(PamhyrWindow):
             },
             data=self._data,
             undo=self._undo_stack,
-            opt_data=self._study.time_system
+            opt_data=self._study.time_system,
+            start_date=self._study.date
         )
 
         table.setModel(self._table)
diff --git a/src/View/BoundaryConditionsTemperature/Edit/Table.py b/src/View/BoundaryConditionsTemperature/Edit/Table.py
index 812cc5ec..a29937b3 100644
--- a/src/View/BoundaryConditionsTemperature/Edit/Table.py
+++ b/src/View/BoundaryConditionsTemperature/Edit/Table.py
@@ -87,7 +87,9 @@ class TableModel(PamhyrTableModel):
                 if self._opt_data == "time":
                     value = timestamp_to_old_pamhyr_date(int(v))
                 else:
-                    value = str(datetime.fromtimestamp(v))
+                    value = str(
+                        self._start_date + timedelta(seconds=float(v))
+                    )
             else:
                 value = f"{v}"
 
@@ -104,6 +106,10 @@ class TableModel(PamhyrTableModel):
         column = index.column()
 
         try:
+            if (self._data.header[column] == "time"
+                    and self._opt_data == "date"):
+                value = self.date_to_elapsed_seconds(value)
+
             row = self.get_true_data_row(row)
 
             self._undo.push(
diff --git a/src/View/BoundaryConditionsTemperature/Edit/Window.py b/src/View/BoundaryConditionsTemperature/Edit/Window.py
index 5d875d3e..0c7306a4 100644
--- a/src/View/BoundaryConditionsTemperature/Edit/Window.py
+++ b/src/View/BoundaryConditionsTemperature/Edit/Window.py
@@ -117,7 +117,8 @@ class EditBoundaryConditionWindow(PamhyrWindow):
             },
             data=self._data,
             undo=self._undo_stack,
-            opt_data=self._study.time_system
+            opt_data=self._study.time_system,
+            start_date=self._study.date
         )
 
         table.setModel(self._table)
diff --git a/src/View/LateralContribution/Edit/Table.py b/src/View/LateralContribution/Edit/Table.py
index 2c1e87ce..330d2092 100644
--- a/src/View/LateralContribution/Edit/Table.py
+++ b/src/View/LateralContribution/Edit/Table.py
@@ -76,7 +76,9 @@ class TableModel(PamhyrTableModel):
                 if self._opt_data == "time":
                     value = timestamp_to_old_pamhyr_date(int(v))
                 else:
-                    value = str(datetime.fromtimestamp(v))
+                    value = str(
+                        self._start_date + timedelta(seconds=float(v))
+                    )
             else:
                 value = f"{v}"
 
@@ -93,6 +95,10 @@ class TableModel(PamhyrTableModel):
         column = index.column()
 
         try:
+            if (self._data.header[column] == "time"
+                    and self._opt_data == "date"):
+                value = self.date_to_elapsed_seconds(value)
+
             self._undo.push(
                 SetDataCommand(
                     self._data, row, column, value
diff --git a/src/View/LateralContribution/Edit/Window.py b/src/View/LateralContribution/Edit/Window.py
index 6b01d249..62329aef 100644
--- a/src/View/LateralContribution/Edit/Window.py
+++ b/src/View/LateralContribution/Edit/Window.py
@@ -109,7 +109,8 @@ class EditLateralContributionWindow(PamhyrWindow):
             data=self._data,
             undo=self._undo_stack,
             trad=self._trad,
-            opt_data=self._study.time_system
+            opt_data=self._study.time_system,
+            start_date=self._study.date
         )
 
         table.setModel(self._table)
diff --git a/src/View/LateralContributionsAdisTS/Edit/Table.py b/src/View/LateralContributionsAdisTS/Edit/Table.py
index 5975c875..51d2540b 100644
--- a/src/View/LateralContributionsAdisTS/Edit/Table.py
+++ b/src/View/LateralContributionsAdisTS/Edit/Table.py
@@ -90,7 +90,9 @@ class TableModel(PamhyrTableModel):
                 if self._opt_data == "time":
                     value = timestamp_to_old_pamhyr_date_adists(int(v))
                 else:
-                    value = str(datetime.fromtimestamp(v))
+                    value = str(
+                        self._start_date + timedelta(seconds=float(v))
+                    )
             else:
                 value = f"{v}"
 
@@ -107,6 +109,10 @@ class TableModel(PamhyrTableModel):
         column = index.column()
 
         try:
+            if (self._data.header[column] == "time"
+                    and self._opt_data == "date"):
+                value = self.date_to_elapsed_seconds(value)
+
             row = self.get_true_data_row(row)
 
             self._undo.push(
diff --git a/src/View/LateralContributionsAdisTS/Edit/Window.py b/src/View/LateralContributionsAdisTS/Edit/Window.py
index 174cc644..f828dc8c 100644
--- a/src/View/LateralContributionsAdisTS/Edit/Window.py
+++ b/src/View/LateralContributionsAdisTS/Edit/Window.py
@@ -124,7 +124,8 @@ class EditLateralContributionAdisTSWindow(PamhyrWindow):
             data=self._data,
             undo=self._undo_stack,
             trad=self._trad,
-            opt_data=self._study.time_system
+            opt_data=self._study.time_system,
+            start_date=self._study.date
         )
 
         table.setModel(self._table)
diff --git a/src/View/Tools/PamhyrTable.py b/src/View/Tools/PamhyrTable.py
index dc8920fb..9748a13d 100644
--- a/src/View/Tools/PamhyrTable.py
+++ b/src/View/Tools/PamhyrTable.py
@@ -19,6 +19,8 @@
 import logging
 import traceback
 
+from datetime import datetime
+
 from tools import trace, timer
 
 from Model.Except import NotImplementedMethodeError
@@ -59,6 +61,14 @@ class PamhyrTextDelegate(QStyledItemDelegate):
 
 
 class PamhyrTableModel(QAbstractTableModel):
+    def date_to_elapsed_seconds(self, value):
+        """Convert an entered date to seconds since the study start date."""
+        entered_date = value
+        if not isinstance(entered_date, datetime):
+            entered_date = datetime.fromisoformat(str(value).strip())
+
+        return (entered_date - self._start_date).total_seconds()
+
     def _setup_delegates(self):
         if self._table_view is None:
             return
@@ -85,7 +95,8 @@ class PamhyrTableModel(QAbstractTableModel):
                  undo=None,
                  opt_data=None,
                  options=["rows_selection"],
-                 parent=None):
+                 parent=None,
+                 start_date=None):
         super(PamhyrTableModel, self).__init__()
 
         self._table_view = table_view
@@ -102,6 +113,7 @@ class PamhyrTableModel(QAbstractTableModel):
         self._options = options
         self._undo = undo
         self._lst = []
+        self._start_date = start_date
 
         self._setup_delegates()
         self._setup_lst()
diff --git a/src/View/WeatherParameters/Edit/Table.py b/src/View/WeatherParameters/Edit/Table.py
index 996ef4b7..59191551 100644
--- a/src/View/WeatherParameters/Edit/Table.py
+++ b/src/View/WeatherParameters/Edit/Table.py
@@ -77,7 +77,9 @@ class TableModel(PamhyrTableModel):
                 if self._opt_data == "time":
                     value = timestamp_to_old_pamhyr_date(int(v))
                 else:
-                    value = str(datetime.fromtimestamp(v))
+                    value = str(
+                        self._start_date + timedelta(seconds=float(v))
+                    )
             else:
                 value = f"{v}"
 
@@ -94,6 +96,10 @@ class TableModel(PamhyrTableModel):
         column = index.column()
 
         try:
+            if (self._data.header[column] == "time"
+                    and self._opt_data == "date"):
+                value = self.date_to_elapsed_seconds(value)
+
             self._undo.push(
                 SetDataCommand(
                     self._data, row, column, value
diff --git a/src/View/WeatherParameters/Edit/Window.py b/src/View/WeatherParameters/Edit/Window.py
index 2e2bb878..d20beaab 100644
--- a/src/View/WeatherParameters/Edit/Window.py
+++ b/src/View/WeatherParameters/Edit/Window.py
@@ -121,7 +121,8 @@ class EditWeatherParametersWindow(PamhyrWindow):
             data=self._data,
             undo=self._undo_stack,
             trad=self._trad,
-            opt_data=self._study.time_system
+            opt_data=self._study.time_system,
+            start_date=self._study.date
         )
 
         table.setModel(self._table)