Try using the users call. There is a response parameter of lastLogin which will be in UNIX time as outlined in this documentation. This indicates the last time the user logged into the organization. You will be able to determine it if this more than 90 days old.
I'm not sure about how to do it thru the API, but there are a bunch of tools that are available for looking at activity/usage and other admin items of interest. If you haven't already check these out...
Tim, the original question was about users....are you wanting activity for local users? Or are you wanting local services (maybe for different thread).
Try using the users call. There is a response parameter of lastLogin which will be in UNIX time as outlined in this documentation. This indicates the last time the user logged into the organization. You will be able to determine it if this more than 90 days old.
