What is the difference between Peak schedule/Off-peak schedule in Android mail application? In Android mail app, what is the difference between Peak schedule and Off-peak schedule
When you setup a Mail for Exchange, the default synchronization mode is Direct Push.  With Direct Push, the device maintains an open connection so that information is delivered to the device as it becomes available.  The setting for Direct Push in Mail for Exchange is called “Always on.”  The alternative is a Scheduled Push mode where the device is set to check for new messages at a set interval.

Though Direct Push offers more up-to-the-minute message delivery, for some users, increased battery consumption may be a trade-off.  If your battery is not lasting as long as you would like, set a Scheduled Push interval by changing the Peak sync schedule and Off-peak sync schedule in Mail for Exchange.

So you can setup high-frequent mail checks with peak schedules for the time periods when you get more emails and off peak schedules when you normally do not receive more emails, (e.g. after office hours.)

Should you require how-to on setting up the schedules, refer this article.