Woohoo! Glad it's still working Triumph
I'd wait as long as possible before you remove the tiles - once his correct toilet habits are engrained then he may be OK but I'd give him as much time as you can as these habits do tend to take a long time to disappear and the moment he does it again you're back to square one. Some cats don't ever forget but given his age hopefully he's more likely to give it up once he starts developing proper toilet habits (and the rest of his habits and personality!) as he's still at the learning age
If you're planning on letting them outside in the future when they're bigger then this will make a huge difference to his toileting habits so if I were you I'd wait until he starts going out before you risk removing the tiles. I know that's probably a long time given his current age but if you can wait it out then it'll be worth it in the long run! Very pleased to hear it's working though, that's fantastic news!
