For those of you who breed multiple females to a single male: how often do you rotate which girl he's with? Do you ever give the male a break?

I have a little 2009 piebald (700 grams) that I'm rotating between a 2009 pastel and a 2008 black pastel. He's been a bit slow figuring out what to do with them he's finally got it now.

So how often should I rotate him between the two ladies? What's the "optimal" pairing period to make sure both girls stay on track? Should I give the pied a recovery period, or just wait until he sheds? (Though he's still not breeding so furiously that he's got a crusty vent or anything like that.)