PPC Software that adjusts for time of day?

Please direct me to some

[beren]

Looking at my site logs, it is apparent that most of the effective visits are during daylight hours in my target market, while paid clicks continue through the night.

I would like to adjust my bids so that I target first or second place during the day, but fourth or fifth at night.

I currently have a bid management system (for Overture, not for Google) but it doesn't allow set up for automatic adjustment of target position based on time of day.

Is there such a system available?

Ideally, the bid management software would

1) Work on both Overture (Yahoo) and Google AdWords

2) Automatically change target positions at times when I program it to do so.

3) Otherwise be programmable so that I can do all sorts of seemingly random bid changes without actually being at the computer.