I have created a planner (Day mode) that has a DisplayUnit of 5 mins ie 12 per hour etc.
I then create an PlannerItem with :-
ItemStartTime := 10:05
ItemStartTime := 11:05
If I then change the DisplayUnit to say 15min and then back to 5min, the ItemStartTime has been changed, ie changing the DisplayUnit to Zoom In/Out of the Planner changes all the Item Start/end Times.