Fifth and Sixth Umbral Calamities: How long did they last?

How long did the Calamities of Ice and Water each last? I haven't been able to find any specific information in Encyclopaedia Eorzea and I suspect they never gave any hints, but I figured I'd ask in case someone saw something I missed.

I know that Umbral Eras do not last as long as Astral Eras, but the "Age of Eternal Frost" is not a name you give to an event that is over quickly. On page 29 of volume I, it was said to have lasted "years" but nothing more concrete was said.

I found similarly vague information about how long the Sixth Umbral Calamity lasted.

On page 47 of volume I, the timeline says that the floodlines were receding as early as ten years into the Sixth Astral Era. It also shows that the population of Eorzea finally began to bounce back around the year 350, with massive migrations described on page 36 (Age of Communion section) from "islands beyond the Bloodbrine Sea" as well as Othard and Ilsabard to Aldenard. This was also when the three great hyuran migrations into Eorzea took place.

It makes me think that, if it took four hundred years for remote populations to explode enough to force migrations, something was happening world wide to keep those populations low for a century or two. It could have been internecine warfare or wars for resources, I suppose. The Spanish Reconquista took about 700 years, and during that time, the Moors being pushed out of Spain would have been sequentially moving to other parts of the world.

Even if it wasn't the flood keeping people from moving around or expanding, it's an interesting three hundred year gap.

Thoughts / data / things I missed would be greatly appreciated.