So today I learned that it is possible to set an alarm in the future for the motherboard to wake up and a poweroff - and the ability has been around for years (since around 2000)!
This article - https://www.linux.com/training-tutorials/wake-linux-rtc-alarm-clock/ - gives a great demonstration on how to set real time clock wakeup by playing with /sys/class/rtc/rtc0/wakealarm. Some good pointers on cleaning out any BIOS based wake ups as well
This article - https://www.maketecheasier.com/alarm-automatically-power-on-linux/ - introduces the command line tool rtcwake which is a little more user friendly
