If the idle circuit is correct, it shouldn't be effected by the timing. Idle speed on the other hand will be effected. The idle circuit needs to be adjusted at a speed below any mechanical advance. It may be nessessary to change idle speed as you adjust the idle screws. If you don't have the idle circuit right its hard to get the rest correct. The idle circuit is always in play. What you want is the throttle plates closed as much as possible at idle rpm. Also each idle screw is its own circuit. They don't have to be adjust in and out the same. One may be out 1 turn and the other will be out 2 turns. I usually start out 5 turns (rich) and screw them in 1/4 at a time. I am looking for a 20 rpm per screw.
Timing should be set with no vaccum and low enough so you don't have any mechanical advance effecting it. If it is not stock, stock setting don't work the best. Trial and error.