Are you still feeding the tank? These fish need to go on a hunger strike. NO food for 3 or 4 days until the ammonia doesn't spike up like that.
What is the stocking in the tank? If it is a nearly fully stocked tank, than it is more than likely that it did spike up that fast. The reason that 5ppm ammonia is suggested in the fishless cycle thread is because a fully loaded tank can produce 5ppm or slightly above in 24 hours. So, in 2+ hours, an increase of about 0.5ppm is very likely. The first thing that you need to do is lower the fishes waste output by not feeding them. (This also helps if you have been overfeeding as well, because any scrap they don't eat turns into ammonia eventually as well.)
Keep up with the water changes. In my opinion, you should be doing 90% water changes from now until you can keep your ammonia level under 0.25ppm. Unless the ammonia is under 0.25ppm, do 90%. The exposure to high levels of ammonia can have long term consequences, so the less they are exposed to the better. If your reading is under 0.25ppm but still noticeably the wrong color, do a 50% or more water change. Eventually, this routine will break and you might actually go a day or so without needing to do a water change. But, it will take some time.
What dechlorinator are you using? I'd suggest one that deals with ammonia and converts it to ammonium, like Prime or Stress Coat+, any little bit helps!
Do you have any live plants? Adding some waterweeds like elodea/anacharis will help as well, after the initial melt. These plants can actually use ammonia directly from the water, and help keep the levels down. During the initial melt though, be sure to vac out any leaves that are dying back while the plant acclimates to your tank and lighting. These little guys don't need to be placed into the substrate - they can just float, or you can just bury the stem into the substrate. Either way works. If it gets too tall, trim it and put the trimmed end into the substrate. These plants do in fact grow like weeds, so fast growth will be another good ally in this. Once your cycle is finished you can drop them, but this will help to give your filter bacteria a bit of a helping hand keeping up with the ammonia. Keep an eye on your nitrates. That will tell you if the bacteria are processing ammonia or not. Eventually, even with the plants, the nitrates should start to climb a bit (not much, given all the water changes, but if you are watching closely you'll see it).
