I am using flex time for a couple of months now and in my case it really improved my workflow. How I proceed with the editing depends on the quality of the recorder tracks. If the drummer is OK and on time there is generally no problem and sice the hits aren't that much off grid there close to zero artifacts. I am keeping my edited drums in a separate session, when I am done with the edits I export all tracks to a new session and we proceed with the recordings. When the drummer is bad I simply try to edit that the hands are in time, nearly completely discarding the kick track. when I have finished with the editing I redo the kick track and simply high pass the overheads and rooms.