Hi, Erik! Unfortunately, it's impossible to predict when or if a free dining offer is going to be made. I can tell you, however, that when it has been offered, it has usually been during low crowd times.
Disney Mom Erin gave an awesome answer to figuring out what promotional offers have historically been offered and when. If you click
Disney Mom Erin's Answer, it may give you just the information that you need.
And the free dining offer is always made to the general public. There have been times when Disney Visa cardholders are offered the free dining first, but it eventually becomes available to the general public.
I hope you have a great time whenever you go!