You can try the following steps.
Chef Server doesn't store this information.
You'll need to manage it yourself, possibly using a handler as linked above in the comments. A simple option would be to make a handler which stores the duration of the last run as a node attribute, but the sky is the limit. If you want something to help debug long runs once you find them, check out my poise-profiler cookbook.
I hope the above information would be helpful to you.