It all has to do with two words most casual baseball fans don't know exist: super two. It's a number of days a Major Leaguer is in the bigs before he qualifies for arbitration.
Here's how MLB explains it:
Under the rules of MLB, players with between three and six years of service time, as well as the top one-sixth of players with between two and three years, qualify for arbitration after every season. Those top one-sixth are known as "super-two" players, and that one rule is why we've seen teams so cautious about promoting prospects in April and early May during recent years.
Tim Lincecum was called up on May 6, 2007. That is two years, 148 days. The seven-day difference will cost the Giants a massive chunk of cash.
Lincecum is expected to ask for something in the $10 million range. If he wasn't super two eligible, he would be lucky to get a $1 million contract. Is he worth it? Quite possibly, but we will have to see what happens on the field in the coming years.
On the other end of the "super two" spectrum is the Diamondbacks' Mark Reynolds who was called up on May 16, 2007. That was three days too late to be "super." So instead of multi-million dollar deal, Reynolds could get as little as $500,000 from Arizona.