First up, two definitions:
When is a player eligible for salary arbitration?
A player with three or more years of service, but less than six years, may file for salary arbitration. In addition, a player can be classified as a "Super Two" and be eligible for arbitration with less than three years of service. A player with at least two but less than three years of Major League service shall be eligible for salary arbitration if he has accumulated at least 86 days of service during the immediately preceding season and he ranks in the top 17 percent in total service in the class of Players who have at least two but less than three years of Major League service, however accumulated, but with at least 86 days of service accumulated during the immediately preceding season.
When is a player eligible for free agency?
A player with six or more years of Major League service who has not executed a contract for the next season is eligible to become a free agent.
In the 2011 season, there are 182 days (March 31 through September 28). For every day a player is on the active roster or disabled list, he accrues one day of service time; in any given season, a player cannot earn more than one year of service time. One full year of service is defined as 172 days, however, a player who is optioned to the minors for less than 20 days receives credit for a full year of service. This year, Day 20 is April 19. Zach Britton could pitch in Baltimore on April 20 and the Orioles would gain one extra year of club control before he is granted free agency. Since the O's are likely to control Britton's innings pretty tightly this year (he threw 153.1 last season), he'd likely be the 5th starter. Buck probably won't send his 5th starter to the mound until April 10, and then again on the 16th. The number five slot comes due again on Thursday, April 21, at which point Britton could pitch in the big leagues, having missed a mere two starts, and the O's will gain one extra season of control. I'm hoping to do the math sometime this week (been really busy), but that seems like a really great trade to me.