Normally after the Before Start checklist, at T minus 5 minutes, the FO will ask "Would you like to turn on the APU?". If you do not do the Before Start checklist prior to then, he doesn't ever ask. If you do do the Before Start checklist later, you can say "Yes please" without him asking, and he will turn on the APU, but you have to read his mind to know that's what he wants.

In addition, if you delay too long before saying "Yes please", he will pull the ground power prior to the APU being on the busses, resulting in the dreaded battery power situation.

 

My suggestions are: 1) Have the FO ask "Would you like to turn on the APU?" immediately after finishing the Before Start checklist, if the checklist was done late. 2) Do not disconnect ground power until the FO puts the APU is on the busses.

Looking at the code for Voice control as I type this...

"Happy to start the APU?" is triggered (with a 15 second delay) at the end of the Before Start Checklist  or "holding at flight deck windows and cockpit door" if using SOP 3.

The ground power is not automatically removed, however, PMDG will automatically remove the ground power when the chocks are removed.

Chocks are removed at time remaining = 0, but the APU must be in the on position.

If the APU is not in the on position, the chocks won't be removed.