Hi Shypoet,
Not sure what you mean by waiting for the tank to filter overnight...?
Once you put a fish into its the tank it does not leave it again (unless you need to move it temporarily to a special hospital or breeding tank). The fish stays in the tank while you clean it and do partial water changes - which you'll need to do once a week - but as for filtering, that goes on 24/7 with the fish in the tank.
Possibly you mean the initial tank set-up? You would need to have the tank up and running for at least a week before you put a fish in to give the water a chance to settle down and for the temperature and equipment to stabilise. Then you need to cycle the tank, which takes a about a month.
Have a look at this link on the basics of goldfish-keeping:
Guide to Keeping Goldfish Hope this helps.