The corrupt version requires 20 Defence and 20 Ranged, and lasts for 15 minutes of combat. Meanwhile, the normal version requires 78 Defence and 78 Ranged, and lasts for an hour of combat. After the time is up, the item disintegrates. The time restrictions are the same on PvP and non-PvP worlds. It is recommended that you high-alchemise the item before it disintegrates, to regain much of the cost of the coif.
Contrary to popular belief, this item does not degrade while using non-combat magic.