Turns out kegging is not quite as quick as I had thought. I normally keg my previous two batches while brewing the next two. It fills the down time of a brew day quite nicely. In six hours or less I've kegged two and cooked two.
This past weekend I had to keg my last batches but didn't have time to brew another pair. It ended up taking over two hours. One of the kegs I was using was new to me, and so I had to recondition it before I could fill it. But on a brew day that would have not been a problem - I would have still been able to get it done within the brewing timeframe.
I guess if both kegs were clean and just needed to be sanitized and filled, it would have been a lot quicker. But I just hadn't realized how much of a favor I have been doing myself by combining kegging day with brew day. There's a lot of shared overhead between the two operations, such as set up and clean up.