My assumption about the time bubbles were that each #.X series was its own time bubble. I could be very wrong but I feel like with a story-driven game such as FFXIV, that would have been the direction. From the start of 2.0 - 2.55, X amount of time had passed. A few days to a few weeks later, 3.0 comes. Everyone in Heavensward is in a new time bubble.