Is it permissible to pay in advance for 50 hours of internet usage at an internet café?

The scholars stipulate for the validity of ijarah (leasing/hiring) that the usufruct (benefit) and the ujrah (wage/rent) must be permissible and known. So, if internet hours are leased for a permissible use, the contract is valid as long as the duration and the price are known, and it does not matter whether the payment of the ujrah is made in advance or deferred. However, if it is leased for a prohibited use, the contract is invalid, whether the price is paid in advance or deferred.