You’ll have options to set a “first day” and “last day,” or just “first day.” If you want things truly automated, picking a “last day” will trigger the autoresponder to automatically turn itself off the day after the selected date. Of course, in those instances when you’re unsure of your exact return date, it’s best to leave this open-ended. The “out of office” subject line is much less creative and scientific than say, a cold email subject line or a marketing email subject line. More often than not, they’re very plain and simple, like the following:
I include my boss because I have different backups for five or six different parts of my job, and my boss is more likely to know the nuances of which one is the appropriate contact than the person sending the email, so it’s more likely to get to the right person if she redirects than if the emailer tries to guess which one of the six contacts I listed is the one who can solve their problem. (My specialty is the “other things as requested” section of my job description; I’m sort of a jack of all trades around here. :) )

If you want to send multiple messages over different days, make sure each one includes all the information above so there aren’t any questions left unanswered. And remember — no matter how much space you give these notes, you still need to leave enough room for actual emails!
If you don't want the messages to go out right away, select Only send during this time range.