Right, but I found that the adventure gives the PCs more than enough time to do what they need to do (especially if they come in via the attic and don't actually go downstairs) before midnight.
In retrospect, I'm not sure I should have let them off the hook for stealing the magic dagger and handaxe from the archaeology display. While the adventure itself puts them there to tempt the players, it doesn't actually suggest any sort of consequence for stealing them ... but it does explicitly state that the Golden Vault will intervene if the players get into trouble with the law while in pursuit of their Golden Vault quests.