I've checked this out because my cousin wanted to see the FC Bayern Museum last month, and it actually can get a bit confusing. The Allianz Arena is usually open every day for tourists, unless there’s a match or a major event – then it’s ticket holders only. The museum and the stadium tours have their own schedules, too. Museum times aren’t the same as the main entrance, and tours have set time slots, so you kinda need to plan ahead. I remember showing up once on a matchday with no ticket just hoping to look around, and nope, totally not allowed inside! If you want the real deal and want to see the stands, changing rooms, and everything, booking a tour in advance is the safest bet. The best thing is to check their official website before you go since hours change with events and holidays.