That's ok, none of this in linear.  Remember that everything is dynamic.  The A-Bacs might slow down processing ammonia into nitrite, giving the few N-Bacs time to slowly work their way through the nitrite better than they did in the previous couple of days and the plants might also pick up a little and absorb a little more of the nitrate.  All kinds of confusing stuff can go on.  Your job is just to keep testing and recording and posting and then re-dosing if there's a day when the ammonia finally gets down to zero ppm.
Pick an "Add-Hour" as your time you will always dose the tank.  It is one particular hour out of the 24 hour day and you want to pick it such that later on in the fishless cycle you would be able to do an additional test at the opposite 12 hour time.  For instance, you might choose 7pm as your 24-hour mark, then 7am could be your 12-hour testing point later on.
Once ammonia finally does drop down to zero ppm, you don't care what hour it was when that happened, you still dose the new ammonia at the "Add-Hour."  Its ok if the tank reads zero ammonia for a bunch of hours that day, in fact its good.
~~waterdrop~~