The stadium doesn’t look very exciting from the outside, behind tall security fences. It’s actually a really cool experience. Pay the few euros to go up in the tower and see Helsinki and sports complex from above. An hour should be plenty of time to check out the stadium and go up in the tower, however I did not visit the sports history museum portion. Side note: there is what appears to be a really nice hostel in the complex if you need somewhere to stay a night or two.