Dizneenut has the right idea.
It is very tricky. Sign in about 3 - 5 minutes before the scheduled time and click on the Rewards tab, then click on Shopping Spree.
Continue to refresh until the prizes come up. Click on the prize you want and go through the steps to get that prize. I'm pretty sure you need to get to the second or third screen before you will actually get the prize you are seeking.
You may not get it the first time, but you will have filled in all the necessary information and will be able to wiz through it the next time.
I've gotten many rewards this way. Even three in the same rewards time. Which I must admit was bad, I prevented someone else from getting that reward. (I did two for me and one for DH that day.) They sent me one for me and one for DH. They will NOT let you get two prizes on the same account in one day. But that will send more than on prize to one address for one shopping time.
Good luck!
Lori