There are currently 9 dungeons in WoD and these can be entered at anytime from 00:00 to 24:00 (Server Time)
Each of these dungeons have 4 difficultiy levels: Easy, Hard, Elite and Heroic (for level 70+ players).
You can access the Dungeons 5 times a day at the Easy, Hard or Elite level, given that you meet the level requirements. You can access them more often depending on your Star Level. Once you reach Level 70, you can, in addition to the 5 daily entries for each dungeon, enter any Dungeon at the Heroic difficulty once a day.
As per the pictures to the right, you can view the dungeons from the Dungeons tab in the Daily Events Interface (U).
By accessing 3 Dungeons, your Daily Activity Points (AP) scale will increase by 15. Open the Login Rewards interface and go to the Activity Rewards tab to see how many AP you have earned today.