Using the RTC SQW pin to interrupt the Arduino

[nickgammon]

Do you mean, you want to sleep for most of that second? Or is it not that complicated?

I have some writeups on timers here:

Gammon Forum : Electronics : Microprocessors : Timers and counters

You could set timer 1 to interrupt you once a second. However that won't work so well if the CPU is asleep.