This is what we did on a recent project. The times were left at UTC with a hover tooltip (JS with a fallback to title="Coordinated Universal Time") and we used

This is what we did on a recent project. The times were left at UTC with a hover tooltip (JS with a fallback to title="Coordinated Universal Time") and we used the "timeago" plugin for jQuery http://timeago.yarp.com http://timeago.yarp.com . So far, no complaints.