Here, take a look atPRSCustomizer
. Among other things, it adds a clock on the bottom status bar that updates when you refresh the page.
This does require you replace the firmware with a customized version however. For a very detailed, step-by-step with pictures guide to actually flashing the firmware, have a look at Valloric's very detailed guide on changing fonts
. If you don't want to customise the fonts on your reader, skip to Step Two: PRSCustomizer in the guide and ignore the font stuff.