It will. Any minute now. The smell and the ammonia starts when the organisms ROT, not simply die. I mean when a cat get hit by a car, it doesn't start to smell the moment it died. But in about 3 or 4 days, then holy c'moly! I think you see where I'm going, lol.
You shoulda had at least some ammonia though.
And just to be very sure have another source test your ammonia to make sure your test isn't bad.