If you want to schedule an overnight inactive time, for example 6pm (18:00) till 6am the next morning (06:00), you currently need to set two separate schedules.
This is because the first time (when the system turns off) must be smaller than the second time (when the system turns back on).
For 18:00 - 06:00 you need to set two inactive schedules as follows:
18:00 pm - 23:55 pm and;
00:00 - 06:00 am