On our honeymoon, we had lots of money to spend and we literally spent the whole day there and then had dinner there at WPC and then went to Cirque. (We did get a later start than most days, arriving at 10 or so.) That seemed to be the right amount of time. So, if she's a serious shopper, I wouldn't plan much else that day. Make an ADR at one of the fantastic restaurants at DTD and you won't have to worry about what time it's for. You can just shop around it.
Now, we typically just spend a 2-3 hours there one evening because there's not much we want. We get our tree ornament, some custom stuff from Goofy's Candy Co., and browse.