Hard to tell.

I agree those episodes are linked. I've long been convinced of that It's impossible to know if Jordan would have told them in parallel or not, I'd say they'd probably would have happened close in the book, maybe not intercutting one another, but it's clear that vision belonged in the section of "utter darkness" of Rand, anywhere between the death of Semirhage and the meeting with Tuon.

As TGS stands, though, Aviendha's journey in the ter'angreal happens significantly later than the meeting between Rand and Tuon.

But there's really no way to tell. Brandon has admitted he's altered the various timelines and shifted events around to be able to split the book.

It's more or less obvious, I think, what he did. He absolutely wanted to fit Egwene's story and Rand's as one book and end with the Tower reunion and the Epiphany. The problem is that Jordan had rather set things up in KOD so he wouldn't have to return to Egwene's storyline and Mat's/Elayne's/Tuon's early in AMOL (their last episodes in KOD pushed them all quite ahead of Perrin and Rand), while he had set things up to start AMOL with a Perrin section, then a first Rand section.

Brandon seems to have stretched the beginning and middle of Rand's section (the one for which RJ left very little but an outline) quite a bit. That's likely because of the difference in "plotting" styles. Brandon has needed a lot more "episodes" than RJ would have to include everything for Rand, and the nature of the episodes he created for Rand forced him to add many extra days to the timeline. To wait for messengers etc.

That caused him some problems. He ended up with a gap in Egwene's storyline, which RJ had detailed a lot more than Rand's, and for that storyline he was bound by a date, that of the dinner with Elaida. Brandon solved this by splitting her story. He had one dinner happen on RJ's date, and had the plot development of RJ's dinner scene rather took place at a second dinner scene, much later in the story (we just know Brandon split the scene in two.. so likely RJ's scene was the dinner with Meidani who reported to the BA hunters/Sitters afterward what Elaida had done to Egwene, now in a cell).

Then he had another problem to solve: extending Rand's timeline had pushed the date on which Tuon and Rand met very much. Because of how long it would take for Tuon's raid to reach Tar Valon, Brandon added a few gaps in Egwene's storyline, "well over a month" here, "a few weeks" there etc.

Then in TOM he needed time again, to give Egwene and Rand a "pre-Merrilor storyline". He probably did this by inventing the storyline of the extra bloodknives (if he didn't created them plain and simple as some suspect) and the hunt for Mesaana. As Egwene and Rand were by then in sync, to accommodate Egwene's storyline I'm pretty sure he created this gap of a full month between the meeting of Rand/Egwene and Merrilor (which isn't terribly logical... Rand feels pressed like hell, but he goes and gives Egwene 30 days to write a few letters to pressure rulers, several of which like Darlin, Gregorin, Perrin's group, the Borderlanders were already mobilized, to come to Merrilor... Egwene could have dealt with that in a few days with Travelling...).

To make that happen, he stretched Verin's delay (and he ended up making a mistake, the # of days set in the letter are not reconciliable with the date Mat finally leaves for Ghenji), delayed the meeting between Elayne and Mat, etc. Then Perrin ended up with tons of delays in his storyline as well... the Asha'man get wounded, bubbles of evil to deal with, Galad and Perrin always end up delaying their answers to one another by a few days, and the trial also got a long delay because of a bubble of evil etc. This meant what RJ had set up in KOD, that the Asha'man would be weeks before they could travel again because they had totally exhausted themsselves waiting too long before they decided to tie up their gateways, no longer worked to hold Perrin as long as the plot needed in Altara. I very much suspect Brandon invented a second dreamspike in order to solve this, and this is how Perrin ended up coming to Tar Valon twice, once on the night of Rand's epiphany, and weeks later to incidentally help Egwene with Mesaaana. RJ's version, I suspect, was more succinct: everything took place during the exhaustion of the Asha'man (which perhaps was truly extended further by the bubble-of-evil snake bites), and Slayer wasn't there to protect a dreamspike but had been sent to try to kill Perrin by Moridin after Masema failed and got killed. On the night of Rand's epiphany, a few days after Egwene reunited the Tower, Perrin pursued Slayer to Tar Valon where Slayer made him lose his trail by jumping out of TAR, leaving Perrin in the middle of Egwene's fight with the BA. Then Perrin witnessed Rand's epiphany, had his trial, his Asha'man at last rested and experimenting with the women in mixed circles he forged the Hammer, saved the WC from the army the Shadow had sent after Slayer's failure and they all moved to Andor and met Mat the Asha'man sent to Ghenji, as Rand met Egwene in TV and he told her they'd meet at Merrilor something more credible given his urgency, like in ten days. Graendal, as many suspect, would have had nothing to do with Perrin, as his storyline would have been way too advanced when Rand destroyed Natrin's Barrow. I'm sure RJ planned to have her punished directly for failing with Rand and for Aran'gar's death.

The result of all this stretching of timelines to accommodate the book split and to expand Egwene's story line beyond her meeting with Rand, and Perrin's and Mat's so they'd have enough material to form a second book forced Brandon to delay Aviendha's departure for Rhuidean as long as he could, because Aviendha had to return to Rand only on the eve of Merrilor. The compromise Brandon seems to have made was to give her a storyarc in TGS (Typically RJ would have dealt with her in a single pre-Rhuidean POV), stretching the whole "she won't be sent before she says she's a WO" thing. He also had to de synchronize the meeting with Tuon and her vision, otherwise she'd have spent way too long in the Waste or would return too soon. Such as it is, even by delaying departure Brandon had to stretch it further by having her walk from Cold Rocks, and go into the desert to mediate after the second vision, and even then the vagueness of his timeline markers allowed him to cheat further (by some fan-established TGS/TOM timelines, Aviendha was gone for over 60 days... meaning she spent 30 days or so "meditating"!).

All that stretching is also responsible for many "oddities" in the minor storylines, like Rand's troops spending forever doing nothing in Tear, Logain appearing to have vanished, the 47 WT envoys spending forever waiting at the BT, Pevara being gone for way too long without the Reds being alarmed etc.