The average time spent on your site is the amount of time spent browsing it. A high bounce rate indicates a low average time spent on site. It implies that users are not staying long enough to perform the appropriate action to meet your business objectives.
Using Google Analytics, it is estimated by dividing the total time of all sessions (in seconds) by the number of sessions.
The average time spent by a user on your website can help you know whether your contents are consumable.
The standard average time a user can spend on a website is about 2-3minutes. These few minute are what determine whether your content is enough to leave them with a good impression.