Run the following shell script from init.d (or /data/adb/*.d/ in case of Magisk). Or run directly from init's .rc file. See How to run an executable on boot and keep it running?
# ignore signals
for i in $(seq 64); do trap '' "$i"; done
# seconds until today 3AM
SECS=$(( $(date -d '03:00' +%s) - $(date +%s) ))
# if today's ...
I solved by myself so I'm sharing so it might be useful for others.
Deeper disable wifi/radio = recompile android Linux Kernel disabling wifi/radio drivers
First I tested the Lineage OS custom ROM for my device.
From that I got access to fully rebuild my Custom Lineage ROM. They have all source code for all supported devices including the source for the ...
I downloaded Android's SDK Platform-Tools, extracted the platform-tools folder and ran a terminal in side that directory. When I executed ./fastboot reboot fastboot it did boot into fastbootd successfully. What's weird is that I installed platform-tools, put it in my /etc/ folder, and added it to my PATHS only 2 days ago. I'm not sure why exactly this worked....
Android does not offer this feature by itself (barring restart confirmation after applying system update).
It is possible that OEM customized ROMs or custom ROMs provide this feature. If you're device is rooted, it is possible - one way I am aware of is using GravityBox Xposed module