Originally Posted by
Catapult
Edit edit: It is probably worth underscoring how the term umbral era is a bit misleading. The German translation, as I mentioned above, uses the term "catastrophe" to better articulate what is going on.
Ergo, umbral eras last as long as their catastrophic impacts are being felt, making them typically measurable in years, and astral eras last however long it takes for the next significant world-altering catastrophe to come along, which can be a long time. In the case of the sixth Astral, approx 1573 years.