Dayparting PPC Campaigns
There are many techniques for improving advertising campaigns particularly with robust systems such as Google's AdWords program. Some of these techniques are considered to be advanced, but I find that often they're advanced more because they're not commonly used rather than because they are necessarily effective.
Adjusting a campaign either by changing bids or by deactivating some ads entirely based purely on the time of day is called dayparting. It is considered by some to be an advanced campaign management technique. Dayparting is often turned on because of some analysis that shows bids are too costly for a given time period or because ROI as measured by conversions is too low. And of course sometimes it is turned on just because of a gut feeling.
The funny thing with dayparting is that if everyone did it, its effectiveness would disappear. This is because the cost associated with a particular ad is directly related to the number of competitors there are for the particular ad slot. So when someone pulls their campaign at a particular time, the number of competitors decreases. If enough people do this, the side-effect is that the cost of an ad slot decreases since it requires a smaller bid to obtain a top position. Likewise, when the campaigns are turned back on, the cost will rise back to where it was.
The point of all of this is that I think there's a good chance that dayparting will eventually become less effective as more and more people use it. And more and more people will use it as the feature becomes a standard feature with campaign management tools. I'd say that search engine marketing professionals i.e. agencies are already tuned in to dayparting leaving just the in house folks who may have yet to flip the switch. In the meantime, continue to use it if it works for you. Also consider looking for patterns in your data that show when OTHERS are dayparting and therefore may point to opportunities for you.