Thanks for the thoughtful reply. It is not the amount of time I want to adjust. There is actually a way to do that in the DND settings on the iphone.
My question was about the change in DND operation after the last update (version 7.2). Before that update, when I set DND from the iwatch I had the options you list, but instead of "On until this evening," I had "On until tomorrow morning," and when I selected that feature, the DND icon (on the iwatch) turned purple. It worked great, but that doesn't happen since the update.
As I've experimented further, it seems that the "on until" options change depending on when you try and set the DND. If you do it during the day, it gives you the "until this evening" option; if you do it in the evening it gives you the "until tomorrow morning" option. Entirely possible that it worked this way before and I just didn't notice.
I've also discovered that when I select the "until tomorrow morning" option it actually sets the DND, it just doesn't turn the icon purple. If you want to verify, you have to look at the phone. That icon DOES turn purple if I do any of the other settings. Not sure why Apple would choose to make one option operate differently but guessing it is just a bug. That's why I hate doing updates--they always seem to break something that was working just fine.