I reckon 500 hours + on Undisputed 3 and you should be good to go...
Gold! The question you should be asking yourself are you truly ready for this. First are you beating up all the competition in Muay Thai. Cuz there are tons of champion Muay Thai fighters who've crossed over and become successful AFTER learning the ground game. For those who havn't...well then you get the likes of Pat Barry, Kongo, or Brandon Vera.
Focus on what you're good at first to see where you're at. If you ain't kicking peoples' asses then how far do you think you're really going to get in MMA. I've told this story once I think...and I'll tell it again. One of our guys in our gym who knocks out the competition regularly went into his first MMA fight and got submitted within three minutes. You know what I'm saying...
Marcus Aurelius: Tell me again, Maximus, why are we here?
Maximus: For the glory of the Empire, sire.
Baked, not fried... the healthy choice.