I have to confess not being 100% sure if the timing is set with vacuum removed (and plugged) or left attached on a Load-o-Matic distributor.

Certainly it's off on the later ones.
Idle speed for an auto is set with the handbrake firmly on, and the car in Reverse or 1. Don't rev the motor as it may over-run the handbrake!

The engine must be up to temp (thermostat open) and otherwise dialled in. Dwell is set first if you still have points, not Pertronix.
In working order you first gap the plugs, then set dwell, then rough-set idle speed, then correct base timing, then finetune idle speed. Lastly, adjust idle mixture and rebalance idle speed as it changes.
I forgot to add:
You set idle speed with a small load on the motor. This is so the car doesn't stall on a wet night... Run your high-beams, wipers (pop the arms off the glass), blower fan, radio and blinker while setting idle. It places a load on the generator or alternator, which translates as extra stress on the motor. Naturally when you turn these off, the idle will go up a few RPM. Similarly, slipping into neutral or park will hear revs increase; it's normal.