The easiest way for a user to change their Out Of Office or Holiday message can be done through outlook or via the Outlook Web Access from anywhere.
1. Login to Office 365 Portal (https://login.microsoftonline.com) . Use your EMAIL ADDRESS and your LOGIN PASSWORD.
2. Click the Gear icon at the upper-right corner of your mailbox, click Options
3. Click organise email tab, and then go to automatic replied page
Then you can create Out of Office messages with a start time and end time so it turns off and on automatically as well.
Thanks
Mark