netmeg - 5:03 pm on Aug 9, 2010 (gmt 0)
I have had clients who wanted to change their bids based on time of day and day of the week. It's called dayparting. It's not new, although the people who have asked me to do it were mostly reacting to perceived competitor behavior rather than actual ROI.
But it's a common strategy in AdWords. You may have some new advertisers who use it, or an old advertiser who just discovered it.