If you have a counter on your blog, you will be able to track many things about the people who come to visit you. On Statcounter, the one I use, I have the option of viewing visit lengths, which is, how long each person stayed on my blog. I'm sure this option is available on many other counters as well. One thing I notice as I view my statistics is the tendency for guests to stay for less than five seconds on the days I neglect to post a new blog. This makes sense -- they came to see me yesterday, and today they're checking to see if there's something new. When they discover the same blog at the top of the list, they move on.
You can increase the length of your guests' visits by posting a new blog every day. It doesn't have to be something horrendously profound or life-changing, just something new and interesting to put a smile on their faces and make them glad they came by to see you. And you'll find your stats improve quite a bit.