I understand that a corporation will be putting out contracts to us mercenaries to assist in taking over and defending a planet, but what I'm unsure of is exactly how this becomes a "match". What I mean by this is, will there have to be defenders on planet nearly all the time to prevent from waking up the next day or coming home from work to your planet taken over? Or is there some sort of notification saying "in 2 hours a battle for your territory will begin, start recruiting!"? I have only played EVE fairly briefly, so this may be something easily explained by a system in place that I don't know about, but I have been curious on this point.

There are roughly dozens of districts on a planet. EvE corps hire teams of mercs, defenders and attackers. These mercs take out each district individually, and whoever wins takes the district. Whoever owns all the districts owns the planet. Whenever the mercs hit the ground is when the fighting begins. You get a timer (usually short due to jump gates) telling you how far away you are. Its not always mutual. Whenever the attacker hits the ground is when the battle begins. Defenders can vary. Any other questions?