Just as an addition to Meatdawgs post above - I highly recommend skipping the Golem phase after the second megaflare.

Push Darnus to 80% hp (not below) wait for a dive.
when he goes up - do not send your DD to push him, everyone gather at the bottom with a Thm (one on the ledge still ofc)
When the screen flashes, everyone hits their buffs and the thm does aoe sanguine.

Darnus lands and everyone burns him! all the dd's have their cooldowns ready and should have TP'd on the golem that he spawned during the dive.

We normaly push 30-35% damage in this phase, more than the 20% required to skip a golem phase

also note: we do this for every dalamud dive, The dd's running up and down and burning their cooldowns on a def-up darnus didnt help our timer at all, letting him regain 2-3% hp and hitting the party for 600damage each is nothing compared to the damage dealt by 2 dragoons with their cooldowns ready!