The promotion runs from 4 PM to 8 PM local time at participating locations. You can find a list of participating locations on their website here.
The deal is limited to one sub per person. The sub selection includes the #1 through #6 plus the JJBLT. They normally sell for around $6 or so. You have to order in-store as the $1 subs are not available for delivery.
Photo via Jimmy John's.