Considering the only other grindy phase after the unbrite phase is light farming, which can also be done quickly if you jump into the right content for it--especially during bonus windows--it's entirely plausible for you to finish it in the 2 weeks before SB. The Singing Cluster step is ridiculously easy, as is the 270-275 step.

It will give you a decent weapon until level 66-67, and possibly provide a jump start to the SB relic by allowing you to skip the first phase of it, like how the Zeta weapons allowed you to skip crystal farming if you traded one in.