A few weeks at least.
And the ammonia content of the water is going to get real high in a tank that small, make sure you change the water a couple times a day. The only fish I lost due to bad water was a betta while I wa trying to cycle my fist tank (a two gallon - which convinced me that 5 gallon tanks are the way to go, and that fishless cycling is the only thing my stomach can tolerate)
