Trying to gauge how long something will take your party is an impossible task. I had 90% of the first session of a new campaign get eaten up by an unlocked door with no handle that was just needed to be pushed somewhat firmly. They ended up building a makeshift handle out of debris and accidentally opened the door while trying to hammer it in. I nearly fell out of my chair laughing when they realized that they had never even tried pushing it.
Lol. That was a game with friends.