The 21-day DPN clock starts on the issue date—not when it hits the desk....

https://mighty-wiki.win/index.php/What_is_the_fastest_way_to_triage_whether_a_DPN_is_lockdown%3F

The 21-day DPN clock starts on the issue date—not when it hits the desk. Knowing the difference between lockdown and non-lockdown notices is critical for immediate advice. This guide breaks down the nuances so you can triage fast and keep options open.