I have a guy i am acquiring in trade who was called up to the bigs after 25 games three seasons ago. He spent the last two seasons entirely in MLB and then was sent down to AAA near the end of last season. He still has an Option left. His service time is 2.161 season. His salary this season is $378K

If I start him in AAA this season and then call hip up after 25 games, will he be an arb guy next season....or still pre-arb?

Guessing you are in preseason mode. The other team already did the work for you by keeping him down for 25 games. You don't need to start the guy in Triple-A. He will be arbitration-eligible next season unless you keep him in the minors all season. Arbitration kicks in after 3 years of major-league service. The decimal point you see is days. So this player has 2 years, 161 days of major-league service. There are approximately 185 days in an HBD regular season.