Using a DS3231 RTC alarm + MOSFETS to turn on a MCU
This is a less than desirable design to be switching the GND line of the MCU subsystem. A far more suitable design would switch on the VCC of the MCU section and keep all the GND reference connections tied together.

Switching of the Vcc in the situation shown for a 3V setup could also be a bit simpler in that the job could be done with just one P-channel MOSFET. The P-channel MOSFET would need its GATE pulled to GND to turn it on and that is just what the RTC chip does on the SQW/INT pin.