Check the time on the panel itself is correct as I understand this what controls the on/off timer not the screen pc.
Also check the screen pc clock is correct and the server pc time is correct especially after daylight saving change.
On our version of mip the holiday setting etc. does not function, just the basic on/off time and dates.
If you still cant get it to work there is an alternative method of inserting a 'blank' period into the schedule that will turn the actual lcd panel off for that period of time but leave the screen pc running, there is some info about that somewhere on here, look for 'blank screen' or something similar..