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The ad scheduling allows you to turn your ads on and off for every day of the week.
I save money when i turn on ad scheduling because i'm not paying for some guy on the other side of the world who is just surfing around, or some business manager who is doing research right before bed rather than at his desk in the morning. I've found success.
The best way you can determine the best times is to test. Keep your ads running as often as your budget will allow for a time and then take a look to see where your majority of clicks (and conversions) happen. Take those times and turn on your ad scheduling for those times. Pretty simple, although it never hurts to turn off ad scheduling periodically to make sure you're still scheduling the right times.
I have a med/sci audience and a lot of those people are on early.
Western EU also +25% during lets call it extreme limits of business hours.
China and India I run flat out.
The rest are Toast at the moment, at least for me.