Oregon store hours are fairly standard compared to the rest of the continental United States. Major department stores or shops in the downtown areas including Portland generally follow the 10-to-6 rule, but you should always phone ahead if you have your heart set on visiting a smaller shop. Never assume that a store is open on Sunday, even in the major cities; many smaller shops have truncated Saturday hours as well. Thankfully, coffeehouses tend to keep regular and long hours, so you'll have no problem finding one to kill time in if you have to wait for a store to open.
Note that bars in Oregon close at 2 am, with last call coming as early as 1:30.