With ProZinc, you can shoot 15-30 minutes early each cycle, as long as the number is rising.
And above 200 or more.
Re your ss - we urge new diabetics not to shoot under 200 , but to wait 20 minutes without feeding and retest - to make sure the number is rising and closer to 200. The preshot of 122 was not only very low, but looked like it might still be dropping.. I'd be careful about shooting that low.
You can post on the PZI forum and get advice about dosing. It might work well for Marble to get a lower dose for the lower numbers and a little higher one for the 300s.