Is there a field in the database that captures the last date a user logged into the application?

The database has an entry for current users but it does not keep any information regarding historical access with the exception of some audit trail information from when objects are changed. This audit trail was very limited in version 5 but has expanded significantly in versions 6 and 7. You can however look at the user's log and probably figure out last time the application was accessed by that user. In the current version Asset Reliability has what is called a user actions log which would definitely keep track of most recent access time (and most recent activity) and that can be viewed from the Server Manager but this is only available in version 7 onwards.