Create an online only, hangout event
Create a new event with a date far into the future, like the year 2015. Go to the event's options > advanced and enable 'this event is online only' which will create a unique Hangout URI.
Create a cronjob
Create a cronjob on each device to open the web browser Monday-Friday at 12:49pm and open the unique Hangout URI.
Firefox cron example:
# Run Firefox at 12:49 EST each weekday and open hangout URI 49 12 * * 1-5 export DISPLAY=:0 && /usr/bin/firefox 'hangout-uri'
Chromium-browser cron example:
# Run Chromium-browser at 12:49 EST each weekday and open hangout URI 49 12 * * 1-5 export DISPLAY=:0 && /usr/bin/chromium-browser 'hangout-uri'