No, you have access to the Account type US, which allows you to hold positions overnight and over the weekend; there is no requirement to close simulated trades at the end of each day.
However, for simulated futures contracts, all positions must be closed before the contract expires. If you do not manually close your position before expiry, it will be auto-closed 1 hour before expiry at the current market price from our liquidity providers. Please note that simulated futures do not auto-roll to the next expiry.
Expiry dates are always announced in advance in the Trading Updates section, so we highly recommend visiting that page regularly to stay informed.