I would like to suggest implementing a means of quick access to the numbering counters.
I propose two ways of doing it: a toolbar with the counters, or putting the counters inside the panels for each time instants layer. I'm attaching two image illustrating my ideas, one for each case.
The toolbar would have two text boxes, one for coarse counter and other for fine counter, and maybe a button which shows the same menu as the "Edit > Number new instants with" submenu. Same for the panels.