I scoured the internet to find a RTG casino with fastest payouts that also accepts US players (Im in CA) and found this casino. Its called Casino Extreme. I deposited via bitcoin and there is an approval process to withdraw which took overnight- pretty fast in my experience and after my documents (ID) were verified and approved I cashed out and the money was in my bitcoin wallet within 30 minutes.
They offer a $50 free chip for new players and a 1000% bonus for first time deposit which I wish I took better advantage of. I deposited $30 so got $330. If I had known withdrawal would be so fast, I would have deposited more so I could bet higher on slots for bigger wins. The rest of the bonuses after that are not that good, but they offer free chips after every deposit if you lose which they give the next day. Enjoy!
Edit: I should add that they also have great customer service including a phone number you can call into.