I created a MedWare glossary as you suggested, with the command entry for F12, and it makes life even easier. I hadn't ventured into command entries before. Now that I've tried one, I'll probably add more.
Merit time-stamps each F12 entry automatically, so I don't think I'll need the shorttime/longtime commands. (Unless I'm missing something, which is quite possible.) You can view the automatically-generated time stamps in Merit with View > Toggle Blanks or by pressing Ctrl-B. This displays a window on the right with a listing of time stamps, and you can double-click a time stamp to go directly to that point in the voice file.
Again, thanks!