We will be in Paris for a week during the end of May/early June. My wife and I have been there before a couple of times but this will be a first for my son, who is graduating with an Architecture degree. Consequently, we may or may not go to some of the major tourist destinations. We would like to be able to have a very loose itinerary, but I know that some sites such as a Louvre etc. really require some advance planning.
So I am wondering how much in advance I need to consider purchasing timed entrance tickets for the major sites. 1-2 days? A week? More?
Thanks in advance for any feedback.