You can get an upgraded poetic weapon (i130) in less than 3 weeks if you start at zero poetic balance, less once they remove the poetic weekly cap. Every other (relevant) weapon besides Zeta and FCoB weapons can be had in significantly less time.

There is about 2 and 1/2 months before the expansion. It all depends on how you want to spend that time, but since you play pretty frequently, you could definitely make a Zeta for your favorite job while simultaneously gearing all your other jobs as well.