We've improved and updated the presentation of implementing message tags to Messenger nodes within Flow Builder. Now inside the Messenger node are 3 options: Sent "inside 24 hours", "outside 24 hours window" and "as a Comment reply".
Sent inside 24 hours will be the default setting for your messages and should be used for all initial opt-ins and messages intended to be sent within the 24 hour contact window.
Sent outside 24 hours window are for specific messages like OTNs, Recurring Notifications and Message Tags that are sent after the 24 hour contact window closes. Make sure your messages follow the parameters set for each of those options.
Sent as a Comment reply is a specific message option that should be only used for the Comments Growth Tool as the initial reply after the comment is made.
Learn more about sending messages outside of 24 hours using message tags here.