the voltage regulator uses up unnecessary power
Would a 555 timer be able to do this, or an RTC?
I didn't know you could use an arduino without providing exactly 5 volts. If I use rechargeables AAs, 1.2 * 4 is 4.8 volts. Would that damage the arduino at all?
Also, can you program an RTC to give a pulse every X seconds?
As for a switching supply, I assume that that is a power supply that turns on or off when it detects a pulse? In that case, the RTC would give it a pulse at t = 0, the arduino turns on, then maybe the RTC (or arduino, I guess) sends another pulse at t = .1 seconds or so to turn the arduino off. The cycle then repeats?