Why not sleep, use RTC's square wave output as an interrupt to wake up more often than once a second? Check the time, if not ready to send yet go back to sleep, check again.
You have these choices with a DS1307 for example:
1 Hz, 1000mS
4 KHz, 0.250mS
4 KHz seems like plenty, keep track of where you are within the second using that.
Wake up increment time interval counter, see of power pulse occurred yet.
Waking up every 250uS, or 4000 clocks, I guess you'd stll be sleeping most of the time.
This sounds interesting - have you actually used the interrupt to count time?
It does not matter when I update the data - 60 seconds, 61 seconds etc.... But I need to know how long since the last update to get accurate data durations for the pulse count.
Are you saying with this interrupt I could increment a volatile variable and simulate my own millis function?