T54W display remains black after power saving.

[mighty-tower]

Firmware Version: 96.86.188.9 (Dutch via Lydis)
Hardware Version: 96.1.2.0.2.1.2

Via the web interface I set the office hours on my phone in the power saving settings from 8 am to 6 pm. At 6 pm the display of my device goes out as set, but the next day at 8 am only the background lighting switches on and not the display, so there is nothing to see on the display. The display does not light up completely until I press any button.

I have set the Off Hour Idle TimeOut to 1 minute.
For example, if I press a button at 7:30 am, the display will light up completely, 1 minute later the device will go back to power saving. If the office hours start after this action, the screen will light up completely.

it seems that the device goes into sleep mode during the night, but I can't find a setting for this anywhere, or is there something I might be overlooking?

Thanks for the help.
Peter