You need to read the rules on each site, they are always in the FAQ section.
Most sites do not have a minimum period. CryptoGames charge a small fee for early divestment but that's it from the sites on this list.
That is not a good rule because as an investor can withdraw their money at any time if they think that site may not perform better. If they forced you to stay for some time then better avoid those sites and invest your money in some other sites. You can have a transaction fee but not early withdrawal fee and force people to invest for longer time.
Plus Crypto-Games is 2nd in the highest return on investments. If you guys also noticed I think Crypto-Games is the only site that never touches a negative weekly return on investments.