He should be fine. I definitely waited until I was on T until I started using the mens room. I realize, however, that this isn't an option for everyone, and I didn't publicly make the name/pronoun switch until hormones and surgery had been completed (only my gf at the time knew anything about it). The bathroom switch came naturally along with everything else. I can't even remember fussing about it really, or when the first time even was.
Men are unobservant. I think the safest time to make the switch is when you have women telling you you're in the wrong room half the time you use the restroom.
