A few months. Best thing is to watch the new growths. Let the new shoots come out between 6-12 inches. You can then unwrap the tape to check. Most grafting tapes are biodegradable so you won't even need to unwrap.
I also saw your questions about germinating seeds. I normally soak mine in water for a few days until I get around to put it in potting soil. The seeds that float are no good. You can just throw those away.