diff --git a/SAS/TMSS/backend/services/scheduling/lib/constraints/template_constraints_v1.py b/SAS/TMSS/backend/services/scheduling/lib/constraints/template_constraints_v1.py
index bbef33f9c63e30490f131301adad8679c2f2cd11..a67d5e1fdd93c0ed9202254bc0b1796ca5f87cb3 100644
--- a/SAS/TMSS/backend/services/scheduling/lib/constraints/template_constraints_v1.py
+++ b/SAS/TMSS/backend/services/scheduling/lib/constraints/template_constraints_v1.py
@@ -329,7 +329,8 @@ def get_longest_observation_task_name_from_requirements_doc(scheduling_unit: mod
 def get_earliest_possible_start_time(scheduling_unit: models.SchedulingUnitBlueprint, lower_bound: datetime) -> datetime:
     constraints = scheduling_unit.draft.scheduling_constraints_doc
 
-    main_observation_task_name = get_target_observation_task_name_from_requirements_doc(scheduling_unit)
+    # TODO: for estimating the earliest_possible_start_time, we need the full duration of the scheduling unit, not just the longest one.
+    main_observation_task_name = get_longest_observation_task_name_from_requirements_doc(scheduling_unit)
     duration = timedelta(seconds=scheduling_unit.requirements_doc['tasks'][main_observation_task_name]['specifications_doc']['duration'])
     try:
         if 'at' in constraints['time']: