Just add this to your StartUp and it will remind you about giving your eyes a rest every hour!
You may set your own delay time (default - 1 hour) by pressing a "cog" icon when the window shows up, or you may set it or turn the program off any time by pressing the icon in tray with RMB.
Warning! If you have an active full-screen application (e.g. you are playing DOTA2) it will be minimized when the EyesKeeper shows up!
So make sure you close EyeKeeper before you play some competitive matchmaking (though I think it won't really disturb you in singleplayer/non-competitive games).
This is how it looks like:
