Black Lion News Network - Ticker in-game
Well, world bosses already have their own timers which can be put on an overlay in game. http://dulfy.net/2014/04/23/event-timer/
The temples won’t work because the PvE maps are no longer tied to the server. This means multiple copies of each map are opening and closing all the time and which one you land on when you go there is pretty much random unless you can get a taxi. If 3 of those maps are having different temple events going on and 2 aren’t, how can the timer tell you that and how do you get on the one you want?
The WvW one might work though since it’s tied to servers. There are some apps for that for those that follow WvW, though not in game and has no notifications that I know of.
ANet may give it to you.
no, i do not want more clutter on a cluttery screen. ONLY if it is toggable maybe. seems a waste of resources though, just check the wiki or some other timer site/app