How old is the buck now? He may not produce as large a litter with the second doe, if he's already been "used" today. Can you wait a day and give him time to "recharge"? I prefer to wait 3 days between breedings with the buck. And if I do 2 breedings in a week, I'll let him rest a week before he breeds again.
I would wait a day and then use him again to give him time to rest.
You do know that depending upon what he carries for his recessive genes - you'll most likely wind up with blacks and broken blacks - right? You're not likely to get harlequins or broken harlequins (tris).
It's really better for your buck to give him at least 24 hours between breedings. It's really exhausting for them and you wouldn't want anything to happen to him. (And after using him twice like that, don't use him again for a while.)
Bucks can service quite a few does in one day. We used a buck on 4 different does in one day andall the doesgave birth to nice sized litters.
If you are breeding each doe more than once, breed again within one hour (European studies have shown this is the optimal time if breeding more than once).
Give the buck a couple hour break, then breed the second doe.
:shock: We haven't such luck with our boys! (I do breed back to the same doe after an hour, but won't use the same buck on another doe the same day... the couple times I tried,I got really small litters from the second doe... must be doing it wrong!)
edited to add:I'll give it a try with the next breedings... have a young buck that would probably be up to the challenge.