An "instance in time" is simply the state of all energy at any one moment. I say "all energy" because our reality is comprised of 1) energy in many different forms and 2) space - the container of the energy.
To travel back in time would be to reverse the course of all energy - from the perspective of a segment of the energy. Given the total amount of energy in our reality - that's not very likely.
I feel that Flickr is going about it all wrong. They host pictures, but they lack focus. IMHO they should begin offering ways for their hobbyist audience to make money.
1) Allow companies to post picture descriptions they want, and allow Flickr users submit entries for those requests. Companies can buy the images they want; Flickr makes a small royalty per transaction.
2) Host a Stock Photo interface for users who want to participate. Users who submit entries for photo requests, which are not accepted, can be moved to their stock area.
3) Use their audience to build an online photography service directory - complete with galleries for each photographer represented. Allow customers to book and rate directly through the site.