If he's rolling nonstop every day at instant play, if you go at spacebar speed (holding down spacebar about 200 rolls per minute, without any extra scripting), you will make about 288,000 rolls per day. On average, you'll hit a 1mx every 4 days. And personally I have observed 1mx happen more often than expected (2-3 per million sometimes, closer to 2) so it could be faster than that.
Specbey has 10.7m bets overall, and $1.47m played- so about .07 cents average per roll. So if he's rolling nonstop limbo, and he's doing it on usdt, (6.1m of his bets and 342k playthrough), which is about a .05 cent average per roll and checks out, he should have seen at least about 6. If he's seen less than that, he's unlucky, actually.
Assuming every single roll is going for that ofc...