Change strings???? I never even tune them.
Ok but seriously, gigging guitars usually every four to six weeks, maybe longer if I can get away with it if they don't happen to go dull.
Stopped using FretFast for a time as I felt it gave a false impression as to how good the strings actually were, finding the intonation went off wack although the strings looked nice and new. Also the guitars did get a bit greasy.