Use of Topical Finasteride after FUE (Build up with 1mg oral Finasteride)?

Hey Docs, I am 4 weeks post-FUE surgery and plan on starting with 5% Minoxidil and Finasteride 1mg orally. The plan is to take Finasteride for 90days (1mg) to build up a "certain level" and then switch to a topical solution which contains 5% Minoxidil and 0,15% finasteride 1. IF there were side effects with taking Fin, they most likely wouldn't appear until about 90 days after I start, right? 2. Do you have experience with switching from Oral to Topical Finasteride? Will also have 3PRPs