How long are each ultimate FFXIV?

How long are each ultimate FFXIV? Not just for their mechanical depth, but the scale of things. While your average savage encounter will clock in at around 10 minutes. An ultimate will last you through up to 20 while going through several phases with different core mechanics.

Not just for their mechanical depth, but the scale of things. While your average savage encounter will clock in at around 10 minutes. An ultimate will last you through up to 20 while going through several phases with different core mechanics.