We'll be in Paris in April and want to purchase advance tickets to the Louvre but not sure what day. How far in advance do we need to purchase? Also, I see there are evening hours on Wednesday and Friday. Can you come and go on the same day with one ticket? I.E. Go in the morning for a few hours, leave to do something else and then come back later in the day or evening using the same ticket as in the morning?

Check the official website for ticket availability. It depends on how busy they are.
Ticket purchased is valid for one entry only. So if you leave, you cannot re-enter. Exception is it gives you same-day access to the temporary collections and free admission to the Musée Eugène-Delacroix within 48 hours.

The Paris Museum Card is valid in many places, especially the Louvre Museum. If you are staying in Paris for more than 2 days, it may be the right choice.

And the Museum Pass allows multiple in-outs during its validity.

OK Thanks. I looked at the Paris card. Unless there's more than one, it's awfully pricey.

It sounds like you are talking about the Paris Pass -- that is pretty much an expensive marketing ploy.

What was recommended was the Paris Museum Pass - different animal . . . It is a good. deal IF you plan on visiting several of the covered museums. Museums in Paris are fairly pricey and costs quickly add up if you are visiting more than three or four.

Here is a link to the museum pass:

https://booking.parisinfo.com/il4-of...seum-pass.aspx