diff --git a/custom_components/versatile_thermostat/open_window_algorithm.py b/custom_components/versatile_thermostat/open_window_algorithm.py
index 267efb7..2c4c9e1 100644
--- a/custom_components/versatile_thermostat/open_window_algorithm.py
+++ b/custom_components/versatile_thermostat/open_window_algorithm.py
@@ -16,7 +16,7 @@ _LOGGER = logging.getLogger(__name__)
 MIN_DELTA_T_SEC = 0  # two temp mesure should be > 0 sec
 MAX_SLOPE_VALUE = 2  # slope cannot be > 2 or < -2 -> else this is an aberrant point
 
-MAX_DURATION_SEC = 600  # a fake data point is added in the cycle if last measurement was older than 600 sec (10 min)
+MAX_DURATION_MIN = 30  # a fake data point is added in the cycle if last measurement was older than 30 min
 
 MIN_NB_POINT = 4  # do not calculate slope until we have enough point
 
@@ -46,8 +46,8 @@ class WindowOpenDetectionAlgorithm:
         if self._last_datetime is None:
             return self.add_temp_measurement(temperature, datetime_now)
 
-        delta_t_sec = float((datetime_now - self._last_datetime).total_seconds())
-        if delta_t_sec >= MAX_DURATION_SEC:
+        delta_t_sec = float((datetime_now - self._last_datetime).total_seconds()) / 60.0
+        if delta_t_sec >= MAX_DURATION_MIN:
             return self.add_temp_measurement(temperature, datetime_now)
         else:
             # do nothing