ok there are 86400 seconds in 1 day or there abouts
if you tell the timer to repeat every 86400 seconds and start the timer at 12am then it should in theory repeat at 12am the next day.

/timerbed 00:00 0 86400 /amsg [Auto-Msg] It's Midnight!

i did not test it ...but it should be accurate tell yer next windows reboot (which will prob not be too long <GRIN> )