Why do some federations show an end date?

As a security and audit measure, some federations have added an end date, which can be seen on the Federation Details page of the relevant mint. 

You can access this page by navigating to the Wallets tab and selecting the relevant federation. If the mint has added an end date, you will see a note to the effect of "Federation ends in Xd Xh Xm."

Not all federations have elected to go this route, but the ones that have are either temporary in nature or are planning to rotate to a new federation after the listed end date.

Establishing an end date is an effective way to audit that the amount of eCash issued (liabilities) equals the amount of bitcoin the mint holds in reserve (assets).

Because unredeemed eCash will expire on the listed end date, it is very important that you withdraw all funds from the federation before this time.

That every member can withdraw their funds from the federation without issue is a method for the guardians to prove to themselves and to their users that the mint is fully reserved.