I recently installed (for the first time) my own drop away rest. I feel like it is working well, but how do I know if the "drop" timing is right?

Use spray on foot powder. spray it on the rest and the riser, let it dry, then shoot an arrow. After shooting inspect the rest & the riser. If you see any powder that has rubbed off then you have contact. Be mindful though that you will have a bit of rub where the arrow rubs against the drop away once fired until the drop, drops....