If you want the exact language of how to calculate service time:
Those Player rights expressly set forth in the Basic Agreement for which a Player’s eligibility is dependent upon credited Major League service will be determined as follows:
(1) One full day of Major League service will be credited for each day of the championship season a Player is on a Major League Club’s Active List. A total of 172 days of Major League credited service will constitute one full year of credited service. A Player may not be credited with more than one year of credited service, 172 days, in one championship season. Major League service will be computed commencing with the date of the first regularly scheduled championship season game, through and including the date of the last regularly scheduled championship season game. This rule shall apply uniformly to all Players and all Clubs notwithstanding differences in a particular Club’s schedule.
(2) For purposes of calculating credited service, a Player will be considered to be on a Club’s Active List if:
(a) placed on a disciplinary suspension by a Club, the Senior Vice President, Standards and On-Field Operations or the Commissioner, or on the Disabled List; or
(b) called to active military duty for up to two years or if called to emergency duty by the National Guard for a period of up to thirty days.