At their size, you can move them any time you want. If you take enough of the surrounding soil, I doubt you will see any transplant shock at all.

i would move them when they are dormant .... which means when the leaves turn color or fall off ...

ken

The best time to move them would be when they are dormant (after leaf fall). Your oak may have a relatively very long taproot (depending on what kind of oak you have), so be prepared for that. The link below may give you some good ideas.

Here is a link that might be useful: Planting a Tree or Shrub

Sorry Ken, didn't mean to rreeppeeaatt. You snuck that one in on me.

repetition is the sincerest form of flattery .. or something like that

ken

"Imitation" - ;)

As the other fellows mentioned, waiting for dormancy will insure the best chance
of seedling survival. But if you choose to dig them up now, I would recommend
that you put them in a shady, protected location for about 5 - 7 days after potting.
This should give them time to recover from the insult to their roots (and to begin
photosynthesizing again).

Josh