I think it depends what phase you're in, how long you've been lifting, etc etc
Just go for a goal I reckon! If you don't make it on time, you haven't lose anything, you'll still be some of the way there.
Be careful though because just because you squat 150lb won't mean your jeans will fit again... might be the opposite Having a goal for your jeans to fit again is fine! We're allowed to be a bit vain.