With regard to the time I don't normally run the developer to exhaustion, I replenish so my times remain constant.
I have on occasion an extra roll at the end of the day where I have nothing left to replenish before dunking it. I still do the roll as long as I have enough to cover. Seems to work with either normal and extra time.
In your shoes I'd probably add 15 seconds or so for each subsequent bath and see if that works. I'd also do the more important rolls in the 1st 2 baths.