Lets presume that I have manual backup server (Nas) in a "safe location" offgrid.

The sever runs on UPS power connected to solar. If power level on battery is below 50 % it will send a separate SMS/LORA warning. The server is connected via free-data NMT/LTE POE device connected to my microtec router POE port.

What would be the best way to do it if I only want the sever to be online once a week during lets say 30 minutes and than go off-line. Would it be possible to shedule the MikroTek to "power-on" on a certain time demand and than go to deep sleep until next scheduled time. It should not be able to respond to any ping or wake up command. It should only powered on during these times.

Would it be possible to shedule the MikroTek to "power-on" on a certain time demand and than go to deep sleep until next scheduled time.

Nope, mikrotik is designed to be allways on. There are some devices with extremely low power consumption though (as low as a few watts) ... if that's bearable.

Use power plug with timer.
Easiest solution.

Be carefull with DST though since usually these things to not adjust automatically.