Long ago, we were required to start the APU at top of descent for ETOPS requirements. The worked pretty consistently so the FAA said we could stop.
What we found out was if you turn on the master and allow the door to fully open, it will spin the turbine and circulate the oil, making it easier to start.
Might be a good practice (once you have the STC).
TC
We still do this monthly (start before TOD). Failure to start boots us off the 180 minute rule but I believe 120 is still available.