Many people aren't aware of this, but you don't have to complete and turn-in a dungeon (normal or heroic) daily the day you pick up the quest.
If the quest giver happens to have a good quest you want done, but can't that day... Just pick it up and do it another day. You can turn it in even if the quest giver has another quest as the daily.
I always try and get some of the normal dailies and keep them for when I happen to go the heroic as well. And having Mech Heroic is always good.
This also works with the BG daily.
Common knowledge? Perhaps. Some guildies got surprised when I clarified this for them.