Going to Paris in early Aug with the expected throngs of tourists (yes I know a bad time but we have a free place to stay thanks to housesitting for a vacating local) - wanted to get a sense how far in advance we should book the Catacombs ticket - like to be flexible in terms of weather for other tour ideas so wanting to save the Catacombs for less nice weather times - do we need to book weeks or months ahead to get a morning slot and just pick a day or can we play by ear when we are in the city - same goes for the Louvre as well
You might want to start looking now and see how much availability there is online. That should give you a sense of how much it’s filling up. I’ve felt that most things seem to book up fairly quickly. It’s a trade off - the loss of spontaneity v knowing you can go the places you want to without waiting in line all day (if walk ups are even an option anywhere anymore).