Set bonus for ele ....

(2) Set: When your Lightning Shield is triggered by receiving damage, a charge will be generated rather than consumed, up to a maximum of 3.
(4) Set: Reduces the cooldown of your Thunderstorm spell by 50%.

45s base CD, 35s when you use the glyph becomes 22s and 12.5s

If you box 5 ele shaman you get - when glyphed - you get every 2,5s a thunderstorm ...