As long as you place your pre-order before the pre-order period ends (1), you can take advantage of the offer.
If you use none of your pre-order credit before proceeding to checkout, the Samsung Credit will be saved and added to your cart. Your Samsung Credit will be sent digitally to the email address you provided at checkout 35 days after the last item your item ships out.
If use some of the Samsung Credit on your pre-order, be sure to spend it all before proceeding to checkout. The unused credit amount will be forfeited.