With power auras it's very simple to time it. There is never a point where you NEED DP, it's a spell there to help with your regen especially in hard modes. I personally use it every 3 minutes when my Avenging Wrath/Divine Illumination is off cooldown.
Sorry if I seem a little elitist, but didn't you just say a few posts back that your spells cost more when you get more mana? That to me just deserves a double facepalm.
Oh and here's you an armory link of a top paladin who uses Darkmoon Card.
http://www.wowarmory.com/character-s...7jin&n=Protent (from US 1st Premonition)