When he's better than the guy he'd be replacing in the ML lineup.

I would wait until ST of next season to make the decision. If at that time you believe you can compete for a wild card or your division then it is the time to bring him up and start his ML clock ticking. If  you don't see your team as being competitive then wait until after game 25 next season and bring him up then.

With a team that is 53-78 he is no doubt probably better than some of your present players but why bring him up in what is a lost season with only 30 games of it remaining?

There is value in keeping him cheap through his prime. I would probably give him one more full year of development, then call him up at the 20 game mark.

But you will get different answers from every owner. Tec gave you a different answer, I know mikeT will give a different answer (he loathes waiting 20 games to call up a prospect)

Yeah, 20 games is 1/8th of a season.  If he's a difference-maker, let him make a difference.   If he's not, what's the big deal?  This player is under contract until he's 30 if called up at the start of next season.  He'll likely be declining by then and demanding a 4 year deal. 

I do have a little difference stance on pitchers as they hold their value longer.

My argument, is that you sacrifice 1/8th of the season for an extra year of control.  Getting him to 31, where is still likely very productive.  Then you can let him go.  You sacrificed 1/8th of a year while hes still developing for 7/8th of prime'ish playing time at arb prices.

My final argument, and it holds true with about 90% of HBD owners, is that you're not likely to be around for that 11th season. 

I'm a stick-around kind of owner.  I've saw 10 twice and 11+ three times(my current worlds).   How about you?

thanks for your help guys... I was leaning towards leaving him down for the next full season then bringing him up at the 20ish game mark... Mostly because this team is awful and I have to put a pitching staff together before this team will be competitive

I had to go back and look, lol. But good point. My three teams now are 0, 4, and 9. My first team I hit 21 seasons. I had a 6 in there as well, but most of my other teams I was just helping fill worlds to roll and did 1 or 2 seasons.

OK. So, I want to add my best prospect to the 40-man roster and promote him to the ML team for the stretch run (when rosters expand).
By doing this, what is the actual harm being done? I do not want to demote him after the season and potentially suffer a ratings decline, so he will be staying up for at least the next 6 seasons, I hope.
Have I lost a year at minimum price? Have I lost a year of minor league growth? He will be eligible for the rule 5 draft next year anyway... I am just hoping to find out why this move is so much worse than waiting one more season and adding him after the first 23 games of the year ;-)
Thanks for the advice/ JRNY.