If I sign an IFA late in the season - say, with 10 games left in the minor league schedule, is it better to assign and play him right away or to sit him so that his pro experience will still be zero next year? Does he burn a year of service time by playing a single game or does he need to play a certain number?

By the way, I apologize if this question has been asked before. I vaguely recall a similar topic bring discussed, but I couldn't find it with a quick search.

All you gain by not playing him is that it would defer his R5 eligibility by one season, as playing even a single game will give him a season of pro service time.  He would need to be put on the 40 at that time.

If he's a quality IFA, by the time he's R5 eligible he's probably also going to be ready for the majors, so protecting him from R5 may be a moot point as you will want/need him on your 40 anyways to be placed on your ML roster.

Playing him is better than not playing him, especially if his minor league team makes the playoffs.  What may look like only 10 days on the schedule could be as long as 30 if the team makes a deep run, and result in a full development cycle that he would not otherwise be getting.

Not that you asked but, if he's not on a playoff team, I probably would't play him.    He may not even get a development cycle for those 10 games.  May as well start at 0 service time next season.

My high A team is heading toward the playoffs, though I'm not sure how far they'll go.

A follow up question, if you don't mind: if I play him now, will he develop next year as if he were an actual second year prospect? Or will be play more like a first year prospect? Prospects in their first two years develop way faster than third and fourth year guys, so I wan as many years of good development as possible.

And will he get a boost in the strength ratings (durability, power, etc) either way this offseason? Or does he need playing Time to get that?

Pro years is not a factor in development.  Age, and the delta between current and "true" projected ratings, as well as all the ancillary factors (coaches, playing time, medical/training, etc.) are what factor into development.

The reason why development is faster in the early years is because the players are younger and have a larger delta gap to bridge.

Also, I believe you will NEED to assign him to a roster before rollover.  I believe unassigned players get auto-released at rollover (somebody can correct me if I'm wrong).  So if you decide to NOT play him, you can still assign him and make him inactive.  If he doesn't play in any games, his years of pro service will remain at 0.

The physical ratings should not be affected by playing time.

Thank you. That is very helpful.

Yes, you have to assign him.    And he'll get the physical development at rollover.