Go to this website, https://salemwitchmuseum.com/tickets/ and purchase your tickets early on the day of and you have pretty much free reign on tour times. Fairly short tour, but it is cool, I'd also reccomend going to crow haven corner and asking about the witch walk which is in the evening.
Our visit was impromptu, but we were able to get our tickets online just prior to entry. It wasn't too crowded, but by April there might be more visitors. Ordering tickets early might be best.
Yes, you make reservations online the day of, before you go. At least it was like this in Feb.
You have to purchase your tickets online. You can do it the same day, but you cannot get ticket at the museum.
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