Arbitration clock starts when player is called up to the Major League team for the first time.
Arbitration eligibility begins with the conclusion of a player's 3rd season in the major leagues.
A full year of service entails 172 days on the active roster.
Exception is The Super Two Rule:
Super Twos come from the group of players who have between two and three years service time and at least 86 days service time the previous year. The top 17% of those players will become Super Twos.
The average Super Two has had two years and 148 days of service time the last two years.
Now teams are trying to figure out the date, when is safe to call up their superstar, to avoid the top 17%, so they can delay arbitration for a year, that saves them millions. In Strasburg's case this could save Washington about $8 million.
Now they figure that the cut off date is May 20, but they play it safe so this means late May early June.
the awesome sig by soty
"You should be mindful of the future, but not at the expense of the
moment." - Qui-Gon Jinn (keeper league expert?)