Wait, are you doing a fish-in cycle, or are you cycling with some other source of ammonia?
If you are doing fish-in, then Hallyx is correct, anything about 0.25 in either ammonia or nitrITE is going to hurt your fish, and if it goes too high could possibly kill him. Getting the numbers down to 0.25 or below (but not at 0) will still allow your tank to cycle, but will keep the fish safe as well. It's a balance between providing enough "food" for the BB's and keeping your fish from getting ammonia or nitrite poisoning in the process.
If you are doing fishless cycling, then yes, your ammonia can be higher. But, you also don't want it to be too high, because that will *also* stall out your cycle. I made that mistake the first time I did a bucket cycle. I thought "more ammonia=faster/better cycle!" but it doesn't work that way. :P (Unfortunately, lol!)
If the ammonia is too high, it will take much, much longer for the BB's that eat ammonia and convert it into nitrITE to work through all that food, and same for the BB's that convert the nitrITE into nitrATE.
It's like you're at a buffet, and someone gives you six plates of food. There's no way you can eat all that at one time. So, you eat one plate, then you take several days to eat all the other plates. Ideally, you want them to bring you one plate of food, so that you can move on to doing other things. Same thing with your cycle. The nitrITE BB's only want one plate of ammonia. :)
Does that help? :)