the idea is to catch your level dropping back down to normal level and since you have been running test p you are good there but mast e is a bit different than other enanthate esters where it has a half life of 5 to 6 days. if you were running test e it would be about the 21 day mark but only because test e has a half life of 8 to 11 days. i would go for 14 days just to make sure i was closer to the level you want to be. any HGC at the end of this cycle? makes things a bit easier. this is all just my opinion and what i have found worked the best for me over the years. good luck bro!
VP