Well you want to keep adding ammonia until you have something in the tank creating it.
Only a bit of the shrimp is going to break down during a day. Let's say it would release 6ppm throughout a 24 hr period (doesn't matter much how much as long as it's enough to build your bb). The bacteria will multiply until it can't get any more food, bringing your ammonia to zero. Although the shrimp is constantly adding (just like your livestock will), the bacteria will break it down just as fast.
So when you're cycled, you have 0amm, 0trites, and a bunch of trates. Continue to leave the shrimp in until the day before you get fish. Remove the shrimp do your large pwc
and start stocking slowly.
Did this all make sense?