taken from the disney photopass faq's:
Photos linked to a Disney's PhotoPass I.D. will be available online the morning after the photos were taken. Guests must claim photos within 30 days from when the photos were taken. Once photos are claimed and associated to a DisneyPhotoPass.com account, they will be available for viewing, sharing and purchasing for 60 days from which the account was created. Photos that have been claimed will be deleted from DisneyPhotoPass.com after 60 days.
We viewed our photos the next day. Then 2 days later, we linked more pictures, but didn't view them for a couple of days. One week later, we decided to buy the Epcot picture, after in-park viewing at AK. We were told we could NOT buy the Epcot picture at AK. We could only buy the AK picture at AK. If we wanted the Epcot picture, we had to either go back to Epcot, or order it online (we ordered online after returning home, and received our photo 4 days later) The only difference with ordering online, we did NOT get the 'cardboard frame' that we have gotten in years past when we picked up the photo in the park.
I just logged in again and viewed our photo from our Dec 5 trip.
If you wait to purchase until day 59, then they will be available to view online for an additional 30 days, or so I was told.