Hey! Congratulations on making it this far!!

I did cardio abs right after but there is not a wrong or right way to do it. It just is what works best with your schedule. If you do it right after though just make sure to watch your form even closer than normal because you are fatigued after an Insanity workout. But again--there is no right answer

Right after is great.
If you just miss a day, I would make it up and be caught up by Sunday.

If you miss more than one, I would just stick with the calendar and push my completion date back. Does that make sense?
Do you have a favorite workout so faR? How are your results coming in month 1?