I would not recommend to quit meds before a procedure. Stopping and starting meds can cause a shed or even worse, lose what you have kept.
Meds are used to prevent, slow down or halt hairloss however consult with your Doctor before any procedure regarding this.
Some doctors say Minoxidil may cause more bleeding during the operation ans suggest to stop it 2 week prior the operation.
I can see why Minoxidil may be suggested to stop before an operation but not propecia.