Obviously, the answer is going to vary by case.But as a default, I’ve settled on four minutes. Here’s why:

• In my experience, most panels that eat into your rebuttal time in your opening give that time back in your rebuttal. I haven’t done a systematic study of this, but I’m fairly confident in the anecdata–confident enough that if the panel didn’t give me the time back in rebuttal, I would take that as a signal.

• I rarely use (or want) more than four minutes for rebuttal in a 15-minute argument, and I’m usually fine with less.

• If my opening is going well–that is, if I’m getting questions and the Court seems to understand/accept my arguments–I can always sit down early.

• If the argument is tough and I am making progress, I can confidently use some of my rebuttal time knowing that (1) I’ll likely get it added back and (2) I can make do with less if necessary. The willingness to risk someone my rebuttal, I think, probably signals to the Court that I am taking their questions seriously and am engaged. Also, I might wind up getting more time than the appellee, which is always nice.

• If I draw a cold or completely hostile bench and don’t feel that I’m making progress, I have a face-saving excuse for sitting down at 10-11 minutes.