Considering the 1 minute interval wouldn't it be better for the battery to use a clock implemented in hardware that boots the chip everytime it's needed?
That is typically what you do, microcontrollers have timers and low-power mode(s) which keep the timers running even though the processor core isn't executing any instructions.
I'm not an expert on power optimization, and I don't know how this is done in micro-controllers. But I would think that the hardware clock would be implemented using integrated analog components (capacitor + resistor circuit) rather than digital logic, to avoid repeatedly switching on and off even just a few transistors.
Apparently external xtal is marginally best (http://www.microchip.com/forums/m341592.aspx); which makes intuitive sense, given that it's exactly the same scenario as a digital watch. 32khz crystal; driver; counter; comparator. Few hundred tiny transistors. Consumption probably less than battery self-discharge.