According to NJ.com:

Matsuzaka was officially "posted" yesterday by his Japanese team, the Seibu Lions. That means major-league teams have until 5 p.m. Wednesday to submit sealed, secret bids to the commissioner's office for the rights to negotiate a contract with Matsuzaka.

At 5 p.m. Wednesday, the commissioner's office will inform Seibu what the highest bid was, but not which team submitted it. Based on just the number, Seibu will then have four business days to decide whether to award Matsuzaka's rights to whichever team won the bidding. If they do, that team will have 30 days to negotiate a contract with Matsuzaka and his agent, Scott Boras.