i don't think its that much. in general, the curve of % odds of winning is smooth - unless you are going to push a guy from like 21% to 19% in a 2 way battle - and therefore 0% - that 20->25m is typically not going to mean much. if you don't run press and have at least 70ish stamina, i kinda think you are fine, but if you have a really low stamina guy or run press - or especially fb/pr - there are times i just won't do the 25m - especially if the guy has crappy defense (the rating yes but more the ability) and will be fouling a lot, making it harder to get his minutes (even if they don't foul out, if they play a few mins less because of early foul trouble, it can really make the 25m harder). its too much risk, too little reward.
i would estimate in a cv + 20 hv + 500 ap + ship + 20m + start type battle, where its 50/50 going into it, that the 25m buys you about 2%, perhaps 3% tops, and it could be lower like 1.5%. i wouldn't sweat it too much for big battles. if its a small battle, like roughly promises + 100 AP ballpark, i could see the 25m buying you more, but its still probably going to be a single digit % increase in odds. for players who have a playing time preference, i don't buy the 20-25m makes much more of a difference - it might increase effort by an additional couple %, if you did the 25m early in the process with all your major effort coming later. but there is more uncertainty on that front, for me anyway. i am really not a 3.0 recruiting expert, or even close.