Ambient room light is sufficient for TTM. No need to intentionally keep them in the dark. I feed enough each day to ensure the fish is getting sufficient nutrition, but not so much that I cause a spike in ammonia. However, I do use prime at the 24 hour mark to keep the ammonia in check for day 2 and 3. It was an immediate game changer for my success rate. I feed more heavily an hour or so before each transfer to insure the fish were full prior to the stress of the transfer.