The problem here is that you don't know when a hack will happen. So, it doesn't really matter for how long you leave your cryptos on the casino. But, surely, the shorter the less risky! (not your keys not your money).
You must always assume that when playing in your casino, any violation of their TOS will get you in trouble of course if you happens to play in a scam casino you are surely going to lose your money
You should always have to assume such things and other risks. These days it's hard to discern what a scam casino is so sticking around to old ones are the best course to do instead of changing from time to time or relying on these new casinos, most of new ones are an outright scam.