Use an ammonia binder
ASAP like AmQuel, Seachem Prime or API AmmoLock. Any amount of ammonia is toxic to fish. This article says that in general for freshwater fish, 50% of individuals will die when exposed to ammonia levels of 0.06 - 2.0 ppm for 96 hours.
http://reefkeeping.com/issues/2007-02/rhf/index.php#15
Consider asking your fish store to hold the fish while your tank cycles.
Most of the biological filter bacteria live on surfaces like live rock, sponges, bioballs. Water changes will slow down the cycle (see soft cycling) but will improve water quality which I think is more important right now.
Disclaimer: I'm new to fishkeeping and know little about freshwater.