[thejeff]

You don't cast Burden of Time to affect your closest neighbors. It's declaring war on the entire world. (Except for a few nations and those probably only if you've already allied and cleared it with them.)
It may cripple your neighbors, but if everyone else piles on with remote attacks, teleporters and pitches in to Dispel that's not going to help you much.

It may come to early, but only in the sense that you won't be ready to make use of it when you first research it.