This power good signal transitions HIGH after the VDD1 and VDD3 supplies are within specification. Expansion board and mezzanine board designs must ensure that circuitry does not interfere with the state of the compute module boot strap pins. See
Boot Strap Signal Isolation
for an example isolation circuit.
All rails are off within 2 milliseconds of a power off event.
Power up order of rails +VDD1 and +VDD3 is not guaranteed, but does not adversely affect operability.