Managing car wrap IG

I currently manage the IG of a car wrap shop business. I take the videos, pictures, and post them on their IG. One post M-F, and a mix of 10-30 second reels and pictures showcasing what was done to the car.

Should I be charging by the amount of cars I take content of or charge by IG post?

The shop does vary on the amount of cars that they work on, some days there are no cars to take content of and some days I’d say 3-5 max. So obviously if I were to take content of 5 cars in a day, I would have content lined up for the next couple of days.

Also, the edits are very basic and probably require less than 30 minutes. If anything, finding the right music for the reel is what takes the most amount of time.