Stick to instruct
It's best to stick to the instructions with the z-pack.
The dosing and timing is meant to allow a fairly constant, and set, amount of antibiotics to be maintained in your system. This set dosing allows for maximum effectiveness against the bacterial infection. If you take the z-pack pill a few hours before or after the 24 hour mark, this isn't a big deal. But stay within 4-6 hours of the mark.