How long do I have to cycle my fish tank if im using an old filter from before?

So I have a ten gallon tank that had fish in it last week..then they died from ich because while i was at my dads house my mom won two goldfish and stuck them in the tank with all the other fish. Anyway, I replaced all the water and I took out all the gravel and washed it with a strainer. I put the gravel back in and i put the same decor in. I filled the tank back up and im using the same old filter but i replaced one of the things because it was nasty. But the other one is still in there. I also sprinkled a little food in there. How long should i wait til add the fish?