GS752TPP Timer Schedule Configuration

Hello Guys,
For some reason i cannot configure the Timer Shedule Configuration in a GS752TPP.
I select
Shedule Time: Periodic
Time start: 05:15
Time End: 23:00

Timer Schedule Selection: present date
Date End: No End date

Recurrence Pattern: Weekly
Every weeks: 255 (or no value at all)
Weekly Mode: I select my prefered week days

After clicking apply (once or twice) -> nothing happens
Sometimes the time shedule entry changes from New to 1, but after a screen refresh i'm returned to the login screen and have to restart the whole procedure,  because everyting is gone. 
Is this a firmware ( 6.0.10.5 installed) hick-up or am I settings this wrongly?
Best regards