If the tank is not cycled yet your biggest problem is going to be a build up of Ammonia in the tank to levels that can be fatal to the fish. The best thing you can do now is buy some ammonia absorbing ZEOLITE and put the zeolite media into a pourous bag and string the bag so it hangs under the water return current from the filter. Also put some in the filter if you can. That will help keep down the ammonia until your tank gets completely cycled.
Depending on how big your tank is and how many inch of fish you have in the tank is going to determine how long it will take to build up enough beneficial bacteria to complete the tank cycling process. It also determines home much ammonia build up you can get in the mean time.