CD use and my A.D.D.

[Mhaeric]

So on WHM, I think i've used Presence of Mind like twice.... I have no idea what applications this skill actually has, nor when it's actually appropriate to use it. And cure3, Should that even be on my bar?

Presence of Mind is the same as AST Lightspeed in my view. It ostensibly your Haste ability for when things hit the fan and you need to crank out the healing. Lightspeed is much better at doing that, but it's still worth using PoM in a situation when you need to act fast. That said, the only time I really find myself using it is for Holy spam. This is where PoM is better than Lightspeed, since it doesn't come with the damage down effect that Lightspeed has.

Cure 3 is by far the most potent AoE heal in the game (not counting SCH crit shenanigans. See below.) It does even more healing than Medica II and it does it up front. Medica I doesn't even come close. Its short range, however, means it's only really effective during stacking moves or if you have a lot of melee in the group or the party stays stacked close together. Cure 3 will be your best friend during moves like Nidhogg's Ahk Morn which is a stacked pulsing high damage attack.

On AST; Time dilation, Celestial opposition, and Disable. I get the purpose behind these skills, but again don't understand the best time to use them.

Time dilation and Celestial Opposition are card effect extenders. Since Balance is the best card, it's just best to use it on that if you can. Don't save it though if you're fishing for a Balance and can't get it. As such, I use Time Dilation on cooldown, with exceptions like I know a pause in the fight is coming up, etc. I do save Celestial Opposition for when I've got an AoE card, 2 buffs on 2 players via an extended card, or if I want to extend the duration of my own card. These happen often enough that it's worth saving for them. And to be honest, this usually happens right at the start of a fight because you'll usually be sitting on a good pre-prepared card combo. And then the fight will be over 90% of the time before it's off cooldown again.

Disable is for Tank Busters, plain and simple. Learn what they're called and set the boss to your focus target so you can easily see it even if targeting a player for healing. When you see the tank buster than hit them with Disable. (Scholar's Virus has the same purpose, and both WHM and SCH have access to it. Thus, all healers have access to this type of mitigation and using these two abilities appropriately will make a very noticeable impact on tank damage taken in a fight, even if the tank is using their defensive cooldowns perfectly.)

And for SCH; my one true love.... But for the love of god when the hell do I use ANY of their abilities post 50? Like... legit. besides the AoE heal, I have no idea what to use these for....

Emergency Tactics is great for when you need to fill a HP bar fast, particularly if you already have them shielded and are out of stacks or need them for something else. It basically turns your Adlo into a Cure 2. Given that we don't have heals stronger than 300 potency outside of aetherflow stacks, this can be helpful if you're low on stacks. Especially if it crits, since that results in a 1350 potency heal which is bigger than even 2 Lustrates. An example of how I most frequently use it when a party member is in danger is to cast a normal Adlo on them to stabilize their hp bar from moving around then hit them with an emergency tactics adlo to give the big burst of healing. Lustrate is more efficient for this, but if I know they're not going to die immediately and I don't have anything else pressing to be doing, then I'll emergency tactics it instead of spending a stack on a Lustrate. I don't usually bother using it with Succor, since Succor's healing is so small to begin with. In this case, it's just turning Succor into an AoE Physic. Not bad, per se, but it's kind of meh.

Deployment Tactics is basically Succor on steroids. I.e. a 300 potency AoE shield instead of 150 potency. Its real strength, however, lies in crits. If you crit the Adlo and deploy it with Eye for an Eye then... wow. You've just given your whole party a 1350 potency damage shield, plus all but guaranteed every mob is causing 10% less damage for the next 30 seconds. How to best use it: Hit your target player with Eye for an Eye first, then Adlo, and then Deployment Tactics. Doing it in that order makes it more likely you'll spread a full strength Adlo, since any time spent between casting Adlo and Deployment Tactics can result in some of the shield being lost before it gets spread due to incoming damage. It's great for moves that require stacking, since everyone will be bunched up. It's great for boss ultimates for the same reason.

Dissipation is... lackluster. It's only real use (not counting the now fixed pet swap exploit) is a clutch tool to grant you extra Aetherflow stacks if you really need some RIGHT NOW. E.g. you're out of stacks and your tank is about to die... Dissipation, Lustrate, Lustrate, live another day. That said, I've used it a grand total of once, not counting for kicks, so it's a highly situational ability. It results in an overall healing potency loss, since the loss of the fairy outweighs the increase to personal healing, so using it outside of clutch situations when you don't need the extra aetherflow is pointless.

Broil and Indomitibility should be pretty obvious, and I think you indicated that you understand these, so I won't talk about them.