Yeah. When I think about it it might be 2 mins and 30 secs. And i didnt mean that Shatter and GoD was used together. Just that GoD was good in the old days...
Shatter does ok dmg though, but casting one blizz plus shatter every 2.5 mins isnt worth the dps. If shatter had 10 secs cooldown, and Blizzard was a faster channeling spell , i think it could have been useful. (Like PB + Chill)
However... I think you should get to lvl 70, and try all the 70 feats yourself, and use whatever you like. Download a parser, and test.