In order to track the amount of time between two different events you can use the getTimeBetweenEvents plugin. It allows you to track the amount of time between two different Adobe analytics events.

I believe this plugin is not free , to get this you need to get in touch to Adobe Consulting.

In case you are not willing to work with Adobe Consulting then you can develop your own custom solution.

You can set a cookie when the first event is fired, in that cookie set the time stamp as t1 and when the second event fire set the timestamp as t2. Calculate the time difference between t1 and t2 and populate the value analytics variable.