I don't know if anyone wrote about it earlier, but I have noticed that adcenter offers pretty bizarre ad scheduling.
I needed to setup ad scheduling for one of my campaigns and after selecting proper hours, I noticed that I haven't selected time zone nowhere on my account (so I didn't know how adcenter recognizes what is the right zone).
I sent them an e-mail and that is what they wrote me:
"In regards to your question about timezones, it is dependant upon the time on the searcher's computer. For example, you have set 7am to 11am as one of the time blocks that you would like your ad to be shown. Whenever a person does a search with one of the keywords that you selected and it is between 7am and 11am wherever they are, your ad will show to them. It doesn't matter if they are on the East or West Coast. So if it is 10am on the East Coast it will be 7am on the West Coast in which case people in both areas will be able to see your ad. Since you also selected 11am to 2pm as one of your time blocks, if it is 3pm on East Coast, only searchers from the Central Time Zone and westward will be able to see your ad . So it depends on what time it is on the searcher's computer. There is no need for you to set the time zone as it is done for you. I hope that this information has been of use."