Well what raid CDs do you have? I can't really help you without knowing your comp
Ideally though you should have EVERY raid cd and personal healer cd up for the 5:00 min mark. It depends on your comp if this is possible or not, but for most people it is. I assume you're going Resto Druid / Disc Priest? In that case do priest - red/blue and druid - green. Use all raid CDs early on in the fight (in a way that they are back up later) in order to conserve mana. Make sure it's early enough that they will be back up.
At 4:58 - treeform, barrier, power infusion (on person without blue) and possibly archangel. Basically anything that takes a GCD use here
At 5:00 - use tank raid CDs, they last longer due to Thrall buff so use them first, also healers pop Volcanic Potions
Use tranquility when needed (before treeform and potion wear off though)
That should last you til 5:40 at least.
I have healed it to the 6 min mark but that's with a holy pally, without one I don't know. I think it's theoretically possible but it would depend on your healer's gear, but if your healers have the gear to do that then your DPS should have the gear to kill it in 5:30 or less.