I need to know the total time users spend on my site

If they are users that are logging in, there might be a plugin that would work for your purposes. Perhaps one of these?

https://www.ads-software.com/plugins/user-login-history/
https://www.ads-software.com/plugins/user-activity-tracking-and-log/

Install and activate Simple History wordpress plugin, It will shows the history of users. It provides the information of most important events occrus in wordpress as follows:
– Posts and pages
– Attachments and comments
– Widgets and plugins
– Taxonomies
– User logins, Falied user logins etc
Try to install and activate this plugin to track user activity on the wordpress site

Google Analytics is the tool folks in the know use. There are plugins for it, but it simply requires adding a snippet of code to the site.

I will try the 3 plugins suggested, but i dont think GA provides the service I need.

Thanks a lot ??