The 21-day clock on a DPN starts when it is issued, not when your client opens...

https://www.lawyersweekly.com.au/sme-law/44139-what-solicitors-need-to-know-when-a-client-receives-a-director-penalty-notice

The 21-day clock on a DPN starts when it is issued, not when your client opens the mail. Knowing the difference between lockdown and non-lockdown notices is vital to managing personal liability. Read this so you can triage fast and keep options open.