I just dont understand whats going on with the 24 man storyline

[Zohar_Lahar]

This is not true in FFXIV. It is the origin of Ultima in Tactics, but none of that information can be assumed to be canon for FFXIV unless FFXIV says it is. And in the case of Ultima, we do know the circumstances around her showing up on Hydaelyn. Which is that she's from some other planet/dimension like Omega and Midgardsormr are. We also don't know when Ultima came to Hydaelyn. We just know that Hydaelyn was much stronger when Ultima came as Hydaelyn was the one to seal her initially. Which is something she most likely doesn't have the strength to do anymore. There's also how it seems that Ultima was the inspiration for the Ultima line of weapons in Allaga which suggest she came to Eorzea before the 3rd Astral Era at the latest.

The Echo flashback you see has Orran Durai explaining to Delita that Ajora betrayed Hydaelyn by summoning Ultima. And since he refers to Ajora as "first of the Zodiac Braves," that implies this was a really ancient event.

[Daralii]

The Echo flashback you see has Orran Durai explaining to Delita that Ajora betrayed Hydaelyn by summoning Ultima. And since he refers to Ajora as "first of the Zodiac Braves," that implies this was a really ancient event.

Unless I'm remembering it wrong, the blurb on her figurine says that Ultima was found already imprisoned by the ancient Ivalicians that would go on to found the Church, and that their worship caused her to develop self-awareness. Orran's an unreliable narrator, so he could have confused Ajora summoning her with Ajora granting her freedom.

[Nuach]

The Echo flashback you see has Orran Durai explaining to Delita that Ajora betrayed Hydaelyn by summoning Ultima. And since he refers to Ajora as "first of the Zodiac Braves," that implies this was a really ancient event.

Apologies but I disagree with you here, though my thoughts rely off of some FFT info, I believe that Ajora lived during the late 3rd Astral Era or the 4th Umbral Era, with Ramza and the events of FFXIV's version of Tactics happening during the mid to late 4th Astral Era.

One of the major pieces of of evidence that I have for this is that Ajora is noted during FFT to have lived during a time when ships flew across the sky, and an oppressive empire ruled where Ajora lived, this sounds rather like the Allagan Empire to me, with the 4th Umbral Calamity bringing the end to it (I know that it was the Holy Ydoran Empire in FFT, but hey if it fits). Or possibly during the 4th Umbral Era with remnants of Allagan airship technology remaining in usage for a time until the destruction of Mullonde (by Ajora summoning Ultima) along with said airship technology. I'm not entirely convinced that Ajora was a WoL, but I could see it, so I won't contest it. The 4th Astral Era is mentioned in the EE as a time of great religiousness which used the Allagan Empire as example of the sin of hubris, this very much seems like it fits together with the Church of Glabados and it's teachings, which leads me to believe that Ramza's actions took place during this Era.

Another thing that points towards this timeline is that it wasn't until the actions of Coinach that the Allag's existence was confirmed in the 6th Astral Era, whereas the Zodiac Braves as a reoccurring group are common knowledge culture heroes in the near east of Thavnair, and presumably Dalmasca, pointing towards these events happening after the fall of Allag. The timeline of Ramza's actions happening during the 4th Astral Era also gives plenty of time for the Garleans to be descended from the Gougans, with all the requisite migrations, and still allow them to be a remembered distant golden era by the annals of Garlean history without having them be pre-Allag (because then there would be no reason to remember the mere Gougans when the Allagan reached higher in it's hubris).

This also lines up with the idea of Ajora as the "first of the Zodiac Braves", there would be three major distinct generations of Zodiac Braves that we know of. The first with Ajora, a group that used the auracites during the late 3rd Astral Era, and thus derived the groups name from them, followed by Ramza and his group, some thousand or so years later during the 4th Astral Era, and then during the waning days of the 5th Astral Era the Zodiac Braves that are referenced during the ARR Relic quest, since for that one there is specific references to Nym, the War of the Magi, and the 6th Umbral Calamity. I could very well see some minor generations of Zodiac Braves dotted here and there that claim the name of Zodiac Braves as well, but those 3 are the ones we know of.

As for the timeline of the naming of Ultima, I am of the thought that Ultima was originally nameless, and extremely destructive. Then during the Allagan Empire, Allag learns of the name and destructive potential of the spell Ultima from Omega (as Cid implies), presumably Omega had encountered it during the voyage between Stars, which the Allagans then conflate with the nameless horror that they are presumably aware of from an earlier era (or perhaps Ajora names Ultima himself), and thus we get Ultima, the High Seraph. I am not convinced that Ultima had anything to do with the creation of the Heart of Sabik, it could easily have been a relic from an earlier Astral Era (The Second Astral Era, maybe?), or perhaps the Heart of Sabik is not of the very Star of Hydaelen, perhaps it is something that predates the very world.

Hopefully this wall of text is informative, and elucidates my thoughts on FFT's timing in FFXIV.