A lot of great suggestions here and I would echo them. Drilling the hole, then mounting the switch to the hole is great idea, if your design allows you to do that. WiFi and magnetic switches also work very well.
However, I have been using pre-printed sleds in most of my rockets 4" and under and for my rockets 5" and up, I have been using a switch bracket design that I CNC. In those situations, you have to drill the holes to the switches.
Below are some photos of the switch bracket I made for an 8" AGM-33 Pike. The key to getting a good measurement for your switch holes is to measure radially from the center. In the photo below, the red circle shows how I lined up the switch bracket at the end of the ebay coupler and used a straight edge to measure
from the center of the bracket to make the marks on the coupler. The lines were extended down the coupler and the positions of the holes drawn. Then I checked, checked and re-checked before actually drilling the holes. Also, I initially drilled 1/16" holes to ensure good alignment. The final holes in this case were 1/2". The initial 1/16" holes allowed me adjust the larger holes slightly if I was off in my initial calculations. And, I would recommend using a drill press. Final picture shows that everything lined up perfectly.
At the end of the day, there are just going to be times when you have to drill the holes to fit the switches, so getting that technique perfected is a good skill to have.