If I purchase a 4 day museum pass in Paris, can I use it 2 days, skip a day, then use it the 4th?
It starts the first time you use it/put the date on the card.
If you want to use it day 1 and 2, not go anywhere on the 3rd, and go places on the 4th you can.
What you cant do is use it day 1 and 2, skip the 3rd day, and try to use it day 4 and 5 (making you use it 4 days out of 5).
Its for consecutive days.. so if you skip a day.. you lose that day..
The French have a lot of rules, but making sure that you get in your quota of museums is not one of them. Four consecutive days; no penalty for not getting enough culture.