This guide will show you how to setup an auto-responder:
First, under the settings tab, go to "Autoresponder":
These options do as follows:
Enable auto-responder: Turns on the auto-responder.
Disable responses to indirect mail: This option will prevent you from responding to messages that you are CC'd or BCC'd in.
Limit responses to once daily: This option will prevent multiple responses to the same sender in one day.
The majority of this page will look very similar to when you send a new message, with one exception, the start and end date options.
Enabling this feature will allow you to set your autoresponder to only send on the dates that you configure.
After you have set the dates and times, and also written up your message, hit the "Save" button.