What is the 240 Day Grace?

If the UW filed a timely application for extension of your H-1B, E-3, or TN stay, you can remain in the U.S. and continue employment for the same employer (the UW) for up to 240 days beyond the expiration of your current H-1B, E-3 or TN while your extension petition is pending with USCIS . 

To verify you qualify for the 240 day grace period, a sticker will be placed on your I-797C receipt notice indicating your new work authorization expiration date under the 240-day grace.

Legal citation: 8 CFR Part 274a.12(b)(20)