Originally Posted by Timbo

The way PBS works is, on the first day they spend the entire day taking checking who's got training and vacation in the next month, then they snapshot of your line, as it exists at that time.

THAT snapshot of your line Dec line is what is used for trip awards in Jan. That is also why all PCS (Swaps/drops/white slips) are frozen for a couple days until the bids are done.

If you then swap for a trip that conflicts with your Jan line, the conflicting trip in Jan will be dropped, not sure how quickly they will see the conflict and drop it, but you might be able to PCS something else to un-phuck yourself before they do.