Beelink GT1 Ultimate wake up for scheduled recording


I have a Beelink GT1 Ultimate Android box with CoreELEC on microSD and Android on internal memory. I have connected a TV tuner and use it with TvHeadend.

I have found energy management options for TvHeadend and I would like to keep the android box in standby or sleep mode until the recording starts. The android box should wake up for scheduled recordings.

There is no sleep mode or standby option in the shutdown menu. I have found somewhere on the net that I should replace the default bootloader with u-boot to make standby available. Where can I find a guide for that? Can I boot to Android after I replaced the bootloader?