Board Thread:Online Discussion/@comment-9933564-20170128084414/@comment-1600847-20170203175220

It's ambiguous. In The Shattered and the Lost quest, one of the fragments of the Celestial Mage says to you:

"You who have walked accross planes and defeated Daedra Princes... or do I speak of things yet to come? Time flows differently for us Celestial beings."

It's probably left ambiguous in case you decide to do Craglorn before finishing the Main Quest.