It is best to circulate the water all of the time. If the birdbath is your only mode of aeration, then it should run continuosly also. I would guess that your pump runs the water through a filtration device? The filter itself usually has an area for beneficial bacteria to adhere to which does as much for your water quality as anything.
Leave it all running, clean the serviceable area of your filter regularly, and spend all of this newly found free time working on that Jeepster!
Here is a link to one of my suppliers
http://www.aquascapedesigns.com
and you can also pick up a copy of PONDS magazine at the chain pet stores and learn a lot.