In a player's profile, if you scroll over that player's 'ML Years' number to get his service time, is the number shown the number of days of service he has?  For instance, I have a player with ML Years of 0 and then I scroll over that 0 and the number shows 0.137.  Does that mean he has 137 days of ML service?  And then once he reaches 172 he gains a year of ML experience?  Thanks.

Yes.  The number to the left of the decimal point is his years of service, and the number to the right is his days of service.

It doesn't automatically turn over to a year of service during the season, it only does that at rollover.  So if a guy already had 50 days of service from a previous season, he will start at 0.050.  A full season is around 175 days, so if he spends the entire season on a ML roster, it will show as 0.225.  But after rollover, it will readjust to 1.053.