At least a month or so. I would invest in an established casino that's been around for a long time and put your money in for at least a couple of months before you consider withdrawal.
A month isn't going to be enough to see some good results and profit from casino's. You should let it sleep there for almost half year or if you can go for a year. Investing to bankroll casino's isn't something to be depend to. It's an investment where you will treat it as an excess investment and you will not completely rely on it.