Investing in bank roll or in a casino takes at least 6 months to get a profit because it doesn't that fast like the other investments because it has a low rate of return and it is one of the safest investment so you can expect a low rate in a legit investment. If you want faster return investment then invest in a coin because they are just affordable and volatile to its price and you can easily sell them because they are available in almost all markets.
Investing in casino bank rolls might seem like a safe investment, but after looking at various casino sites and comparing the potential returns based on their house edge (which I know isn't a perfect way to calculate profits), to me it doesn't seem to be worth it with calculated potential returns of between 1-5% each year. I don't consider this to be a worthy investment unless you supply like 1000 BTC to the bank roll. Then the small percentages will yield you a better return. And that's assuming the casino in question makes profit. It could very well be that within the period you invest, they end up losing badly -- thus you lose badly.
That is why bank rolls are safe because they only give small returns in your investment, i think it is fair to get 5% return per year from your investment because that is also the rate of the average investments in the physical world and you need to consider that there is a lot of investor also so the percentage gets low because the gambling sites tries to balance the expenses from maintenance, bank roll and also the profit that will be given into the investors.