In your case, not having recieved the ballot I would follow their instructions. I would also make a photo-copy of the ballot you would be mailing to them, or print 2 copys of the form and fill-out both, retaining one for yourself.
I also would get some kind of reciept-confirmation at the post office, (They will help you) and since your timeline is further shortened (By sharebuilders requirements...) you may have to choose a faster, more expensive type of delivery, perhaps overnight. Priority-mail usually takes 2-3 business-days.
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