Normal Phase
During the first phase of the fight, the boss will hit the raid with 435136 three times and pull them in with 434776 two times. These are the main damage events of the phase and the ones you need to plan to cover
435136 will hit the raid at approximately 0:05, 0:30 and 1:00, while the 434776 pulls happen at 0:40 and 1:15. After the 2nd pull the boss will start his transition into the 2nd phase at 1:30
This is a very short phase packed with damage but you can't freely send all your available cds here as you will still need some of them to cover damage during the 2nd phase. The ideal here due to some events being very close to each other is trying to double dip in our cooldowns to cover several of them at the same time. Say if you use db and sb to fill up your stasis and heal the group at 0:30 to cover 435136, you can then release the stasis to cover 434776 10 seconds after
df is a very good cooldown here because the raid will mostly be stacked in a short line between the boss and the edge of the platform, making it very easy to get full value out of it
Feeding Phase
After a minute and a half of the normal phase, the boss will burrow into the ground and disappear. He will then start running across the platform and do heavy damage to the raid approximately every 10 seconds for 40 seconds. The damage isn't super high but also there is a good chance your raid will be moving around dodging the charges and killing adds so you need to be able to heal it back up while moving and avoiding the charges yourself
After the charges are done, the boss will start casting 438012 repeatedly around every 6 seconds until fully fed. The damage of this scream is decently high and very quickly increases with each cast. The time between the casts makes this ideal to cover with a lb ramp, as you can spread echoes in your raid and consume them with ve a couple of seconds after one scream to heal the damage from that cast, to then cast ec and have your lb be healing during the following one.
Extra Considerations
This is probably the first mythic raid boss you're gonna fight with your new hero talents, and whether you are playing Flameshaper with trailb or Chronowarden with warp, either way your hover isn't exactly what you are used to from Dragonflight.
This is important to keep in mind because the room is covered in 455831 and unlike on lower difficulties touching one of them will stun you for a long time and require your team to free you, wasting valuable dps on a fight that is already incredibly long
As for what of the two hero talents to pick, the choice here is freely yours. Both trees can play perfectly into the timings of the fight and do great on them when played properly and we don't expect to see a huge difference in the performance of one over the other on this particular fight.