You can set up an autoresponder for direct (one-on-one) chats by going to your Settings > Telehealth & Messaging page. Click Edit settings from the Chat Autoresponder section:
Choose the weekday and the time range for your autoresponder (e.g. daily between 5:30PM and 8:30AM the next morning):
Add additional autoresponder periods by clicking Add period in the bottom-left corner.
Your autoresponder will be displayed to any client who sends you a direct message during the period(s) you've set up. The message will be displayed once every 30 minutes.