From 11 am to 3 pm on 4/21/16 only.
https://www.jimmyjohns.com/
Customers are limited to one $1 sub per person, in-store only. All sandwiches No. 1 - No. 6, BLT, Unwich lettuce wraps and Slims are available for the deal. No delivery or online ordering.
You can go through the line as many times as you would like for the $1 sub, according to Jimmy John's website.