After a few interesting experiences recently with Abyssea EXP alliances ... I feel the need to reiterate and spell-out some information:
1. If you're seeking EXP/Time Extension, it's crucial to build up and "cap" Pearl and Azure lights from the start. Almost everyone understands this, but I've seen a few doozies that don't, so let's just start here. It's become generally accepted that 25-30 of each colored light will "cap" that particular light.
2. If you want to raise the minimum amount of EXP per kill, you ALSO NEED Ruby lights. While a group should cap Pearl and Azure lights first, the group should move on to Ruby lights next. Once Pearl and Azure are capped, the FASTEST WAY to raise EXP per kill is to get GOLDEN LIGHTS. If you do not get any Ruby light, your red chest drop rate will be poor (even with capped Pearl and Azure lights), and you therefore won't get many Golden lights from the red chests.
3. For these reasons: Pachypodium and Blood Bats (Tahrongi Canyon) are *NOT* ideal choices for your EXP camp. Yes, they are "squishy" mobs, but neither of these mobs grant ANY Ruby lights. Therefore, for an average EXP alliance, you will spend 3-4 hours to reach 600 EXP/kill, simply due to not receiving Golden lights during the first 2 hours (roughly).
The same average EXP alliance will likely reach 600 EXP/kill in 2 hours when killing a mob that can grant Pearl, Azure, AND Ruby light.