Hey Guys - I'm a veteran in MMO's (played EQ, EQ2, WoW, Vanguard, Warhammer, and thinking about ESO) and use to have a very close guildmates/friends that I played with.
As instances and MOB bosses popped up, or waiting too much LFG, we used a tool called bloon to see when everyone could get on to do instances/dungeons. It's a SMS-based group scheduler (U.S. only, sorry!) where I poll my guildmates to see if they can make certain times (on a recurring basis). Faster responses on SMS but you do need to initially input everyone's phone number or at least invite them through facebook .