You can always invest anytime on those casinos. Most casinos have a minimum of 0.01btc for investing on their bankroll
I dont really think that 0.01 btc is something that is worth to invest. Sometimes there are thousand btc in one site so 0.01 is not really worth it. You could have better chance of getting profit if you just gamble that instead of throwing it away into investment, you wont get any profit because It is like less than 0.1 % of the bankroll
no problems for using a small nominal as it is, sometimes we play just for fun or to focus on getting small results. But you also apply if you want to get stability in gambling requires a minimum nominal 0.1 BTC for every casino we played.