Tracking subscriber last activity

I run an extranet for my organisation and have set it so subscribers (employees) will remain logged into the site until the actively log out. However, this means I cannot truly know how long ago each user was actually active on the site.

Is it possible to add a timestamp to each subscriber’s meta that shows the last time the open a page or post. I am not interested in what they looked at I just want to know the last time they did.

Hope this makes sense.

Thanks in advance for any help or guidance.

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