To address an earlier question, SQW/OUT on the DS1307 is open-drain, so with a pullup resistor to 5V it can drive an MCU input or other logic operating at 5V.
But the lowest frequency for SQW/OUT is 1Hz, so from a power saving standpoint, I'd favor the watchdog interrupt with an 8 sec period slightly. This would only be as accurate as the system clock, but judging from your initial post ("an hour or so"), maybe that's good enough and an external RTC wouldn't be needed.
Another approach would be to use the 1Hz output from the RTC to clock Timer1 or Timer2 externally, this would provide better accuracy than a resonator-controlled system clock. With Timer1 being 16 bits, the MCU could sleep continuously for an hour (actually could sleep for quite a bit longer). With Timer2, it would have to wake about every 4 minutes. But as with the watchdog, the wake periods can be extremely brief if there is nothing to do.
Yet another approach could dispense with the external RTC completely, clocking Timer2 from an external 32.768kHz crystal and implementing an RTC in software. This necessitates using the internal RC oscillator for the system clock, which can work very well for many situations.
Lots of ways to achieve the same thing!