I think they were referring to the Hourglasses as, since there are 4, which are all separate, it would require 8 GCD in order to dot them all with B+M before having to return to the first one to dot again. B + M are your highest potency/s compared to Bio 2 so I guess it makes sense that you would only rotate those two over 4 separate adds. (changes in a good WoD party where you wouldn't have the option to return to the last one, since it's dead so I see where you are coming from in that regard)
T8 is my favorite example of a SMN trying to be bursty and losing a ton of resources, by Baning/Fester. Where as even Doting it up when it spawns (Facetarget) and Ruin is pretty efficient, and saves 2 Aetherflow for the boss, or 2 for the Dread if your party dps is slow.
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Every different pug I join for random FCOB farming I have to change my rotation. As annoying as it seems, it's probably my favorite part of SMN, with how versatile it is in so many different situations.