This plugin was exactly what I was looking for, but in my tooltip hovers, the band/titles of my recent tracks are followed by "(Undefined ago)" instead of a time of some sort. I did just realize that when I'm currently listening to a track, it says "(Listening now)" in place of the "(Undefined ago)" message, but it's the same for the past tracks.
Also, is there any way to get the links to open in a new window/tab using the shortcode?
Here's the shortcode I'm using:
[lastfmrecords user="justbishop" period="recenttracks" count="10"]