any way to tell how long a user has been logged in?

Unfortunately this is not currently possible. We have an improvement request (ID 152721) on the development backlog to add more information such as the session length to the logged-in users list and I've added a positive vote on this on your behalf. Hopefully this will be considered as a future enhancement.

If this question is related to concurrent licenses and you haven't yet configured automatic logout times, see if they would help in your case: Specifying the Automatic Logout Time in M-Files

That would be very useful. Have several customers who would benefit from that feature.

It would also be nice to know which vault or vaults the user is logged into in the event we need to force logout.  We have several vaults on a server that users can access so knowing which vault they are helps in the event we have to do maintenance on a vault.  Thanks

It would also be nice to know which vault or vaults the user is logged into in the event we need to force logout.  We have several vaults on a server that users can access so knowing which vault they are helps in the event we have to do maintenance on a vault.  Thanks