With ProZinc, nadir is often between 5-7 hours after the shot. But yes, it does change in some cats; some cats are pretty consistently low at the same point in each cycle. The only way to find out is to do a curve - which you did - but because it was without insulin, it is hard to get much from the numbers. You can also get a number in that 5-7 range over a few cycles and see if there is a pattern.