For Follow up work order schedule start and end time issue

When the user is creating follow-up work order, at the time of creating we want to update the Schedule start time and completion time for the new work order created.

But as we update the schedule start time and completion time, this time automatically gets updated to '0', i.e. we cant put any positive value it is always 0, could you please let me know if we can update the schdeule start and completion time while creating follow up work order