I didn't think the original (in Chicago) made much sense, the staging at least. And even in New York, I didn't think "Next 10 Minutes" made sense.
I just directed the show (it plays one more weekend), and we've staged it in the round (it's a circle piece, blah blah blah). The only time I had them in the same time period at all was the 20 seconds or so of Next 10 Minutes that they sing together. But there are other times when I had them on stage together, though in their respective time periods. For example, right before "you know what makes me crazy, I'm sorry..." in See I'm Smiling, Jamie has a monologue on the phone. Halfway through I had Jamie go and sit next to Cathy on the opposite side of the boxes that were establishing the pier for her. When his phone call was over and Cathy started singing, Jamie continued what he was doing in his world while Cathy continued in her world. It just so happened that where Jamie was sitting is where Jamie (in Cathy's world) would have been sitting, so we had a cool moment (in my opinion) when Cathy is singing "you, and you, and nothing but you" to Jamie in her time period, but it looks like she's singing it to the Jamie we're seeing. That's one of my favorite moments of our show.
That was much longer than I intended.
Eeeeeeyyyyyyyyaaaaaaaannnnnddddd aaaaaaaiiiiiiiiyyyyyyaaaaaammmmmmmm teeeeeeeelllllliiiiiinnngg yyyyooooooouuuuuuuwwwaaaahh...