The difference between direct and indirect supervisor is the presence of the supervisor. Direct supervision means a supervisor is psychically present.
When mailing a certified letter, a person should expect it to take from three to five days to reach its destination. Depending on how long it takes the recipient to pick up the letter, the process can take up to 21 days. People who send certified mail receive a notification to prove that the letter has been received by its recipient.
Certified mail generally takes as long as it takes for the receiver to be present to sign for it. In your case, I would say about three days, but again someone must be at the location for delivery to sign for it. The mailman will try to deliver it a couple of times, and then it will end up back at the post office for you to pick up there.