@Daft_Freak Just been reading through the powman code that manages this.
Interesting that when "off" the RP2 is set to low power mode, but as far as I can see not using the LPOSC for an alarm timer. Wake always comes from a button press or interrupt from the RTC.
Looks like they were trying different options https://github.com/pimoroni/tufty2350/blob/main/modules/c/powman/powman.c#L141
Anyway - looks like power "off" would be accomplished by doing https://github.com/pimoroni/tufty2350/blob/main/modules/c/powman/powman.c#L398