M4300 and Timer Schedules / time-range Status always goes to Inactive - How to fix?

schumaku First of all thank you for you answer, however

as I wrote previously, the whole timer schedule goes to inactive as soon as I enter the first entry, so this already invalidates your comment.

I've documented the behaviour with a few screenshots:

Add a new Timer Schedule

Add new Timer Schedule

The Timer Schedule is active

The new Timer Schedule is active - but with no Schedules attached yet

Add a periodic Schedule to the Timer Schedule

Add the new periodic schedule to the Timer Schedule by clicking on the <Add> button (not in the screenshot). It makes no difference if I use a day in the past, todays date or some day in the future for "Day Start".

According to the documentation this schedule will run (ie switch off POE) Mon-Fri from one minute past midnight until 7am. 

However:

The Timer Schedule has become inactive

Now the Timer Schedule has become inactive.

What is wrong here ? How to switch on the schedule?

Coming back to your posting, why should 00:00-00:00 not be a meaningful entry?

How else should I qualify that POE should be down on the port for the whole day?

00:00 - 24:00 is not a valid entry and results in an error: 

"Error! Invalid 'Time End' format: 24:00"

Switching on POE for one minute per day (23:59 - 00:00) by setting it to 00:00 - 23:59 seems kind of non-sensical.

The devices (mostly, but not exclusively IP telephones) would start to boot, just to be choked off again almost immediately - not exactly very healthy for the hardware.