Come and get a free wall clock from Freya & Sio!
It displays SL time, and also has a day/night indicator which revolves once every 24 hours.
And it’s free (well, L$1. I’m sure you’ve got that much).
While you’re there, have a look at the usual range of clocks, which all include dual SL and local time, with a user-friendly script for setting your local time and daylight saving on/off.
Freya & Sio