Were you alone? Did you have a mount that made you go faster? Are your battles typically shorter? Do you skip the dialogue? The estimated time given is calculated if you do none of these things. If you answered yes to one (or more) of those answers, it may explain why it was shorter. Still, there is hardly any reason to complain about being fast. It gets you through the story line quicker!
Easier to finish dungeons when you are death because you don't have to run around and find health wisps.
Those dungeon times are just suggestions - they hardly ever take that long unless you fizzle or die frequently; or you are in a group and you have to wait for the rest of the group to catch up, or they take awhile to choose their spells.
