Found this out, you do NOT have to participate to get a Chest, only be in Zone (at least for Stage 1). I was stuck on FP the entire State from 1% to complete and got a Small Chest. Also the Consumable which adds Fire dmg to each attack has a GAME TIME timer of 30 minutes, then they're gone. You can also get multiples of the same damn item from Chests in the same damn Invasion. That's seriously irritating as it could take someone with bad RNJesus luck a very long time to gear out.
And I need to emphasize this again... Low Level Twinks FUCKING RAPE compared to the best geared 100's. I was taking out Elites in 3-4 hits that were killing 100's. I haven't seen a single 100 yet that could burn down any Legion NPC as fast as my 10 Hunter.
EDIT: Just checked my Map, (2) Invasions can be up at once on the same Continent, even though we initially thought it was 1 at a time per Continent.