Also the addon wouldnt need to communicate outside of the game, and wouldnt need data input from slave chars. It would simply be a 00:00:00 in a frame attached to target unitframe that begins a preset countdown with a defined keypress (such as Numpad 2 as I use Numpad 1 to send my /petattack macro to my warlocks). In my case the 2sec needed for my locks to Immolate, and the 3sec needed to shadowbolt. Simply to prevent me from missing my Corruption cast, for instance, because I pressed the key while still casting Immolate since I'm using my Shaman as my main.
1xElemental Draenei Shaman
1xBalance N.Elf Druid
3xDestruction Warlocks