check out tvfool.com to see what antenna you might need to pick up a signal from your local FOX station. You will also need a OTA adapter to get a good signal to your hopper receiver. Many of us here are using the AIR TV adapter.
Not sure how long is limited time is but I believe this started last Sunday. So basically you now have the NFL Red Zone channel if you sub to this package. I'm sure it is just a good will gesture while they work a deal with the dropped RSN that many subs have had to deal with.