This user script inserts the system time in the upper right corner of the browser window.
This is especially useful in full screen mode, where the task bar clock is hidden.
If something is obscured by the time display, select "hide mini clock" from the context menu of the time display.
To set the minimum width for the clock to appear, resize the browser window to that width and select "mini clock set min width" from the "user script commands" sub menu of the greasemonkey menu.
If you move the mouse pointer over the time display, the current date should appear (hopefully in human friendly form). Since I have no idea what is appropriate for your language/region, I could use some help here.
contact me with my user name + '@web.de'