From Trammell Hudson's Projects
The V.st vector boards can be upgraded with a 32.768 KHz clock crystal and a backup battery to turn them into "scope clocks". The 14-bit output gives them an effective "4K" resolution, which is quite nice compared to the jaggy 8-bit DACs of more common scope-clock kits. On a sharp vectorscope like the Tek 1720 it really looks smooth.
The default face is a 24-hour analog with a sweep second hand (updated every 20ms) along with the date and day of week. Source code is in github/vst/teensyv/scopeclock.ino. As always, feel free to hack up your own version!