AtomJump.org

If you decide to set this on a per forum basis within the database (storeInDb = true), you must run

php install.php

once first to add the database field, then within each forum's tbl_layer entry, fill in the 'var_help_is_coming_json' field with e.g

{
   "timeframe": 60,
   "message": "Thanks for your message. Our current response time is estimated at 1 day. Please hold while we get in touch with support.",
   "helperName": "AtomJump",
   "helperEmail": "peter@atomjump.com",
   "comeBackWithin": 86400
}

Find the server at http://atomjump.org/wp/server-user-guide/. Download and install.
Download the .zip file or git clone this repository into the directory messaging-server/plugins/help_is_coming
Copy config/configORIGINAL.json to config/config.json
Edit the config file to match your own timeframes on a per forum basis. You can set the default forum as 'default'.

{
   "phpPath": "/usr/bin/php", //Note escaping the '/' may be necessary
   "storeInDb": false, //Switch this to true if you wish to set this per forum within the database
   "staging": false, //false is to use the staging version of the messaging-server config
   "serverPath": "your/atomjump/messaging/server/path/"
   "forums": [
      {
        "aj": "aj_your_forum_name", //The forum this applies to, 'default' will apply to all unspecified forums in this list.
        "labelRegExp": "^your_specific_forum_string_start",		//Optional: regular expression used for different 'default' messages when there are several scaleUp databases
        "timeframe": "In seconds this message will remain on the group",
        "message": "The message that gets sent.",
        "helperName": "Any helper name for this forum - this will appear as the author of the automated message",
        "helperEmail": "This email must be set, and must not be anyone else's email, so it should be yours as the administrator",
        "comeBackWithin": "This is the number of seconds when the user can come back and not be re-notified. 86400 seconds = 1 day"
      }
    ]
}

Add "help_is_coming" into the "plugins" array of the server's config/config.json file to activate.