Messages "Send Later" function not available in Sonoma on Mac

I followed the instructions below, or tried to.

When I go into Messages/iMessage in Mac OS Sonoma on my MacBook Pro laptop computer, and I select a conversation, there is indeed a " + " plus button up in the top right corner.

However, clicking on the + does not result in an option to schedule the message to Send Later. Instead, there is a drop-down menu of Contacts.

Anyone have any ideas on this?

Thanks.

Schedule a message on Mac to send later - Apple Support

Schedule a message

You can schedule a message up to 14 days into the future.

1. Go to the Messages app  on your Mac.

2. Select a conversation.

3. Click " + ",  then click Send Later. <---Here's where my problem arises.

4. Choose the date and time you want to send your message.

5. Enter a message, then press Return to schedule the message.

The message appears with a dashed line around it and is stored on a server until it’s time to send it—the time appears above the message.