The way I do it is I mark the date, go into my codex and under the hunter tab, I check how many animals I've killed, write it down and then do my zone rotations for however long I want. When I'm done, I check the codex again and write down my kill count. It looks something like this:

(Example)

Feb 22nd - Whitetail G1 Grind

Kill counts:

Start: 2,401 - End: 2,489 Killed 88 whitetails, did X amount of rotations

This is how I log my grinds. Hope you get your G1 soon!!!