I would go with blackjack. With a little bit of luck I might win that 20% in less than 5 hours. Sportsbetting would be a good choice if I'd have more time, 5 hours to bet at any sport makes it way too limited in terms of choices.
I played on Betonline. Deposits using cryptocurrency are available there. It seems that you can also deposit using cryptocurrencies on ACR. In my opinion, Betonline is a reliable site, at least, I haven't had any problems with it.