orbitalair:
Am I right the DS1307 does not have an alarm?
This is far easier if you use a chip with an alarm, like a pcf8563 or another DS part.Then you just set the bit you want, and when the alarm trips you get an interrupt.
easy-peesy.With just a clock you have to always calc times, convert to seconds(midnite being 0) and compare.
I have no idea if it has an alarm or not...