Which game are you looking at going to? Whether you can get tickets will be the biggest variable. Its difficult to get tickets for a Bayern home game, and similarly games where Bayern or Dortmund are the away side. Last year they announced games up to mid April on 15th December, and then games from mid April onwards on the 17th March. They generally seem to be around the same date each year, give or take a week. The only other thing I'd consider is whether there is another game you could go to locally if you're going for the whole weekend, in Bundesliga 2 or lower.