60 minutes is probably a good estimate for an average game with people who are familiar with the rules (and it is really easy to learn.)
However, there are a few factors that can push a game longer than that. There are two "phases" to the game, exploration and the haunt. Initially all the heroes are exploring the house, buffing stats & collecting items. There is a random element to when the haunt starts. When you discover & enter certain rooms, you roll for it, with an increasing likely hood of it happening based on how many of those rooms have been previously discovered. So if they're all buried in the stack of unexplored rooms or if the haunt rolls are just lucky, it may take a while. Exploration is simple & fast, though. The other factor is that there are something like 70+ haunt scenarios, with the scenario being determined by a few factors (which room and what event/item triggered the haunt.) Many I've seen are straight forward. One, however, involved riddles and dragged the game out for far longer. (Although I should admit that all the players in that game were new and not regular board game players. Several had a few drinks in them.)