1. Click 'File' on the top left-hand corner of the ribbon.
2. Select 'Automatic Replies (Out of Office)'.
3. Click the button next to 'Send automatic replies'. This will enable you to customise the message for the reply. To set a time frame for the replies, check the box next to 'Only send during this time range' and select a time range.
4. Click 'OK' to finish.