1) Create a tag and name it as timer tag or which ever you prefer :

2) Select tag type Google Analytics :

3) Select track type to event :

 

4)  Give the category name as per your requirement :  An example, Timer Tag set up for
40 seconds, If user spends on any page more than 40 seconds, the tag will trigger and counted
as an event.

 

5) Given an action name as per your requirement : An example, Measure the amount of time a
user spends on a page to complete a task on {{Page URL}}.

6) Select the label {{Click Text}}: To know on which anchor text user clicked.

7) Finally Create a trigger on timer tag : Name as Timer trigger & select trigger type to timer. Update Event name to gtm.timer, Setup the interval as per your requirement, An example of 40000 milliseconds (40 seconds) & keep the limit to 1 so that you can track one type user action (user behavior) on landing page.

Enable this trigger when all of these conditions true or you can give as per your requirement.

Example : Once user scrolls to 75% of the page and spends time more than 40 seconds, then trigger.

Final output is timer trigger is working fine in preview mode & push it to live :

The data can be captured in Google Analytics to do further analysis of user behavior on landing page.

If I can be of assistance, please do not hesitate to contact me.