So, first of all, Hyjal and Black Temple need to be separated. They were released within 6 months interval back then. And while players back then were much slower to progress - there was still difference. Hyjal was the top tier raid for months, until Black Temple sort of replaced it, because everyone was already Hyjal geared.
And it would prefer it to be that way this time too, instead of dropping Hyjal at the same time as Black Temple, so it’s an off-raid from the very beginning.
So, here is how I’d suggest doing the PvE phases:
Phase 1 - Karazhan, Gruul’s lair, Magtheridon’s Lair, lasting 2 months. It is the time of levelling, reputation farm, and heroic dungeons, so a big part of the time you wouldn’t be raiding at all, depending on your pace. All 2.0 quests up to and including Hyjal ones should be available upon launch, even if the raids are inaccessible, so the flow of raid questing is not interrupted by having to intentionally walk back to the questgiver to pick up the next quest once it becomes available.
Phase 2 - Serpentshrine Cavern and The Eye in Tempest Keep, lasting 1 month. It’s not a lot of time, but people will be hungry for Hyjal.
Phase 2.5 - Hyjal, lasting 3 months - now let’s give people some time to catch up with the hardcores who finished all raids in the first week.
Phase 3 - Black Temple, lasting 7 months - same as back then, yet 7 months is still a lot of time. People will still be farming Hyjal and Black Temple, some will even be still pursuing their Hyjal attunement for sure. Give them time.
Phase 4 - Zul’Aman, lasting 2 months - one month shorter than back then, because I recall it being a minor raid, like AQ20 or Zul’Gurub, there wasn’t much talk about it, people will still be waiting for Sunwell and it will still be pretty much phase 3 - mostly Hyjal and Black Temple farm. So keep it short. Also, Sunwell has to be unlocked, so it will be relevant in part of next phase too.
Phase 5 - Sunwell and Isle of Quel’Danas. The final version, coming with the lifted attunement requirements and Quel’Danas, but with only the first wing of Sunwell Plateau.
Phase 5.1 - first gate opens after 2 weeks
Phase 5.2 - second gate opens after another 3 weeks
Phase 5.3 - third gate opens after another 3 weeks.
So, 2 months after phase 5 launch, Sunwell is completely open.
Now, don’t rush WotLK - keep it up for some time. Private server people are often like “WotLK as late as possible, TBC was the best”.