How strict should I be about Roblox?

My 9 year old is obsessed with Roblox. All his friends play it. I've done some research and yeah there's the whole in-game chat thing which I have disabled. He only plays for like an hour after homework. But he talks about it constantly and I'm wondering if he's getting too into it. I don't want to be the dad who bans everything but I also don't want him gaming 8 hours a day in 5 years. What's reasonable for this age?