After you send certified mail through USPS it takes between 3 to 10 days for the certified mail to arrive to the person you're sending it too.
Most times the certified mail takes only 3 days but you should send the certified mail at least 10 days prior to the person needing to accept the certified mail to allow time for it to arrive.
Certified mail doesn't always guarantee that someone will get the mail as the person can refuse to sign for the certified mail.
But certified mail makes sure it gets to the correct person and shows you that someone has signed for and has accepted it.
Certified mail also costs around $6.50 per certified letter or mail.