When entering a start date, the entered value for time is lost, when changing focus to the end date.
E.g.
Set start date to 14th Feb
Set time time to 10:00
Set end date to 14th Feb (start time is lost)
I assume the cause of the issue, is the date picker does not allow a start datetime to be ahead of the end datetime, but entering dates in reverse order is not user intuitive.