It really does depend on your market, as with most things to do with PPC.
I`ve used ad scheduling before when I was really up against things budget wise, as it stopped money getting spent when I couldn't watch what was happening (do have to get a few hours of sleep a day

).
It didn't make a great deal of difference though.
There are a couple of periods throughout the week where things change, most are easily explained:
12 - 2pm on weekdays - Workers surfing the net using their employers PC's during their lunch break.
7pm - 11pm - People sitting down on their PC's after coming home from work and having dinner.
Saturdays are usually quiet, as people go out and do things in the "real world", shopping, family trips etc
If you are in a very expensive area, advertising after 6pm can be good as a lot of peoples budgets are used up by that time, giving you cheaper clicks.
My best periods at the moment are evenings, I can make very little up to 6pm, and then it calls comes in during the 7 - 11pm period.
You really need to keep a close eye on your sales and CPC costs for a couple of weeks, and it should allow you to see patterns. Log your commissions compared to your CPC costs on an hourly or 2 hours period during the day, and you can get quite a good picture of whats happening.