I remove the tape before it girdles the graft. Usually in a year but you should do it much sooner if your graft is growing really well. It's hard to give an exact time like when it grows more than 1.5ft It depends on how strong it's growing, which direction, and whether it's likely to get broken by birds, squirrels, rats if you took off the tape.
I'd say definitely not before 1-3 months.