diff --git a/cara/apps/calculator/model_generator.py b/cara/apps/calculator/model_generator.py
index 6c545152..006ec25c 100644
--- a/cara/apps/calculator/model_generator.py
+++ b/cara/apps/calculator/model_generator.py
@@ -458,14 +458,10 @@ class FormData:
 
         present_intervals = []
 
-        def hours2time(hours: float):
-            # Convert times like 14.5 to strings, like "14:30"
-            return f"{int(np.floor(hours)):02d}:{int(np.round((hours % 1) * 60)):02d}"
-
         # def add_interval(start, end):
 
         current_time = start
-        LOG.debug(f"starting time march at {hours2time(current_time/60)} to {hours2time(finish/60)}")
+        LOG.debug(f"starting time march at {_hours2timestring(current_time/60)} to {_hours2timestring(finish/60)}")
 
         # As we step through the breaks. For each break there are 6 important cases
         # we must cover. Let S=start; E=end; Bs=Break start; Be=Break end:
@@ -480,8 +476,8 @@ class FormData:
             if current_time >= finish:
                 break
 
-            LOG.debug(f"handling break {hours2time(current_break[0]/60)}-{hours2time(current_break[1]/60)} "
-                      f" (current time: {hours2time(current_time/60)})")
+            LOG.debug(f"handling break {_hours2timestring(current_break[0]/60)}-{_hours2timestring(current_break[1]/60)} "
+                      f" (current time: {_hours2timestring(current_time/60)})")
 
             break_s, break_e = current_break
             case1 = finish <= break_s
@@ -494,22 +490,22 @@ class FormData:
             if case1:
                 LOG.debug(f"case 1: interval entirely before break")
                 present_intervals.append((current_time / 60, finish / 60))
-                LOG.debug(f" + added interval {hours2time(present_intervals[-1][0])} "
-                          f"- {hours2time(present_intervals[-1][1])}")
+                LOG.debug(f" + added interval {_hours2timestring(present_intervals[-1][0])} "
+                          f"- {_hours2timestring(present_intervals[-1][1])}")
                 current_time = finish
             elif case2:
                 LOG.debug(f"case 2: interval straddles start of break")
                 present_intervals.append((current_time / 60, break_s / 60))
-                LOG.debug(f" + added interval {hours2time(present_intervals[-1][0])} "
-                          f"- {hours2time(present_intervals[-1][1])}")
+                LOG.debug(f" + added interval {_hours2timestring(present_intervals[-1][0])} "
+                          f"- {_hours2timestring(present_intervals[-1][1])}")
                 current_time = break_e
             elif case3:
                 LOG.debug(f"case 3: break entirely inside interval")
                 # We add the bit before the break, but not the bit afterwards,
                 # as it may hit another break.
                 present_intervals.append((current_time / 60, break_s / 60))
-                LOG.debug(f" + added interval {hours2time(present_intervals[-1][0])} "
-                          f"- {hours2time(present_intervals[-1][1])}")
+                LOG.debug(f" + added interval {_hours2timestring(present_intervals[-1][0])} "
+                          f"- {_hours2timestring(present_intervals[-1][1])}")
                 current_time = break_e
             elif case4:
                 LOG.debug(f"case 4: interval entirely inside break")
@@ -652,6 +648,11 @@ WINDOWS_TYPES = {'window_sliding', 'window_hinged', 'not-applicable'}
 COFFEE_OPTIONS_INT = {'coffee_break_0': 0, 'coffee_break_1': 1, 'coffee_break_2': 2, 'coffee_break_4': 4}
 
 
+def _hours2timestring(hours: float):
+    # Convert times like 14.5 to strings, like "14:30"
+    return f"{int(np.floor(hours)):02d}:{int(np.round((hours % 1) * 60)):02d}"
+
+
 def time_string_to_minutes(time: str) -> minutes_since_midnight:
     """
     Converts time from string-format to an integer number of minutes after 00:00
diff --git a/cara/apps/calculator/report_generator.py b/cara/apps/calculator/report_generator.py
index b7b1551a..ea22cbb6 100644
--- a/cara/apps/calculator/report_generator.py
+++ b/cara/apps/calculator/report_generator.py
@@ -1,6 +1,6 @@
 import base64
 import dataclasses
-from datetime import datetime
+from datetime import datetime, timedelta
 import io
 import typing
 import zlib
@@ -126,18 +126,20 @@ def img2base64(img_data) -> str:
 def plot(times, concentrations, model: models.ExposureModel):
     fig = plt.figure()
     ax = fig.add_subplot(1, 1, 1)
-    ax.plot(times, concentrations, lw=2, color='#1f77b4', label='Concentration')
+    datetimes = [datetime(1970, 1, 1) + timedelta(hours=time) for time in times]
+    ax.plot(datetimes, concentrations, lw=2, color='#1f77b4', label='Concentration')
     ax.spines['right'].set_visible(False)
     ax.spines['top'].set_visible(False)
 
-    ax.set_xlabel('Time (hour of day)')
+    ax.set_xlabel('Time of day')
     ax.set_ylabel('Concentration ($q/m^3$)')
     ax.set_title('Concentration of infectious quanta')
+    ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter("%H:%M"))
 
     # Plot presence of exposed person
     for i, (presence_start, presence_finish) in enumerate(model.exposed.presence.boundaries()):
         plt.fill_between(
-            times, concentrations, 0,
+            datetimes, concentrations, 0,
             where=(np.array(times) > presence_start) & (np.array(times) < presence_finish),
             color="#1f77b4", alpha=0.1,
             label="Presence of exposed person(s)" if i == 0 else ""
@@ -240,19 +242,21 @@ def comparison_plot(scenarios: typing.Dict[str, models.ExposureModel]):
         if times is None:
             t_start, t_end = model_start_end(model)
             times = np.linspace(t_start, t_end, resolution)
+        datetimes = [datetime(1970, 1, 1) + timedelta(hours=time) for time in times]
         concentrations = [model.concentration_model.concentration(time) for time in times]
 
         if name in dash_styled_scenarios:
-            ax.plot(times, concentrations, label=name, linestyle='--')
+            ax.plot(datetimes, concentrations, label=name, linestyle='--')
         else:
-            ax.plot(times, concentrations, label=name, linestyle='-', alpha=0.5)
+            ax.plot(datetimes, concentrations, label=name, linestyle='-', alpha=0.5)
 
     # Place a legend outside of the axes itself.
     ax.legend(bbox_to_anchor=(1.05, 1), loc='upper left')
     ax.spines['right'].set_visible(False)
     ax.spines['top'].set_visible(False)
+    ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter("%H:%M"))
 
-    ax.set_xlabel('Time (hour of day)')
+    ax.set_xlabel('Time of day')
     ax.set_ylabel('Concentration ($q/m^3$)')
     ax.set_title('Concentration of infectious quanta')
 
diff --git a/cara/tests/apps/calculator/test_model_generator.py b/cara/tests/apps/calculator/test_model_generator.py
index 58c34092..6c5050e4 100644
--- a/cara/tests/apps/calculator/test_model_generator.py
+++ b/cara/tests/apps/calculator/test_model_generator.py
@@ -3,6 +3,7 @@ import dataclasses
 import pytest
 
 from cara.apps.calculator import model_generator
+from cara.apps.calculator.model_generator import _hours2timestring
 from cara.apps.calculator.model_generator import minutes_since_midnight
 from cara import models
 from cara import data
@@ -272,13 +273,8 @@ def time2mins(time: str) -> minutes_since_midnight:
     return minutes_since_midnight(int(time.split(':')[0]) * 60 + int(time.split(':')[1]))
 
 
-def hours2time(hours: float):
-    # Convert times like 14.5 to strings, like "14:30"
-    return f"{int(np.floor(hours)):02d}:{int(np.round((hours % 1) * 60)):02d}"
-
-
 def assert_boundaries(interval, boundaries_in_time_string_form):
-    boundaries = [(hours2time(start), hours2time(end))
+    boundaries = [(_hours2timestring(start), _hours2timestring(end))
                   for start, end in interval.boundaries()]
     assert boundaries == boundaries_in_time_string_form