AC does not turn on right away when I turn it on

That sounds more like you have a system that is a bit low on charge and as the engine heat gets to the R134A and makes it expand and increase the system pressure it starts working. It turns on at between 28-31 psi. Does the compressor cycle a lot as it works?

Anyway if you wish to replace the switch, yes you need to recover the current charge, replace the switch, draw a vacuum and recharge.