I use the HTC supplied Desk Clock app .... There's a function in there that is designed for 'night mode' and shows a dimmed display of time, date and next alarm set time.
Just hit the moon\star icon towards the bottom of the main Desk Clock screen. The display moves around the screen, like a PC screensaver and the screen doesn't go off, if charging.
I use my Desire in a dock on my bedside cabinet every night like this, as a night time clock and alarm clock, works perfectly for me!