ROCK5 ITX wake on lan technically possible?

I am wondering if WOL can be used to start the board.

No. It’s not supported on hardware. The power consumption of ROCK 5 ITX is quite low running all the time.

thanks Jack for clarifying.

is it possible to wake up with timer from shutdown?

If you have something to do wake on LAN, you have something that can also run home assistant. Get a smart plug and set up an automation to turn the thing on.