User - time spent on the site?

Question

PHP

Good afternoon.
Something while nothing sensible climbs into my head, there were ideas, but I would like to see a couple more on this score.
Essence: It is
necessary to keep records of the time spent on the portal by authorized users.
What algorithm would be applied here, what scheme of recording this time should be used?

Answer 1

The simplest and most accurate. Open a web socket connection. When connecting, remember the time, when disconnecting, count and save to the database.