Where do the HW prologue quests start?

[Niwashi]

During the main scenario's 2.x patch quests, I know the story in the later ones serve as a lead-in towards starting Heavensward, setting the stage for what's to come in the first expansion. But which later ones? Is there a clear cut-off for where that arc of the story begins?

I was originally stopping at the end of the 2.0 story, and planned to wait there until I was ready for Heavensward, so I could then go through the patch quests and straight into the HW MSQ. But one of my relic quests requires a run of Snowcloak, which I don't have unlocked yet, since it's unlocked in the middle of the patch 2.4 MSQ.

Now I'm wondering whether I could do some of the earlier patch quests, but still stop short of the ones that serve as a sort of prologue to the expansion. But for that there would need to be a clear cutoff in the storyline at that point, and I'd need to know where it is. Is it just the 2.5 and 2.55 patches that are HW-related or does it begin with 2.4 or earlier? Is there even a clear cutoff point at all besides the one where I am now (end of 2.0 prior to 2.1)?