Well, for most people when you first dose ammonia it just sits there. For some people it only sits there a few days, for others a week, for a few others two weeks and for a very few it just sits there for 3 weeks or longer. Regardless of how long it sits, for more or less everybody it eventually starts to drop and although it can possibly drop slowly the first time, for many people it drops quite rapidly, in one day or two or three and suddenly the have their first zero ppm ammonia reading and for the first time they re-dose their tank.
Now on average, right about the time the ammonia first drops, a little nitrite will appear. It's usually a little slower going upward compared to how fast ammonia comes down but within a few days it has usually "spiked" as high as the test can read and you are in the "nitrite spike" (the second phase out of three phases of fishless cycling.) Of course this is just "average" and for some people the nitrite will appear before or after the ammonia has first dropped.
People often estimate that the nitrite spike phase will be twice as long as the period it took for ammonia to first drop to zero, but actually the length of each phase is really quite unpredictable. The only sure thing you can do is just steadily keep going forward!
~~waterdrop~~