Hi Jennifer!
Yes, the 30 day limit will be either from the date the photos are taken, or the date the add a PhotoPass card to your account.
Here's some info directly from the site:
Photos linked to a Disney's PhotoPass ID will be available online by the morning after the photos were taken. Guests must claim photos within 30 days from when the photos were taken. Photos not claimed within 30 days from which they were taken will no longer be available. Once photos are claimed and associated to a DisneyPhotoPass.com account, they will be available for viewing, sharing and purchasing for 30 days from the date they were claimed, after which the photos will no longer be available.
Note: "claiming" means either adding a new Disney’s PhotoPass I.D. number to your account or logging in to your account after new photos have been added to a Disney’s PhotoPass I.D. number which was already associated with your account.
To view the expiration date of a photo in your album, click to enlarge the photo. Beneath the enlarged photo, the expiration date will appear.
Have a magical vacation!
Amanda