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.
1st Class and Certified Mail is delivered at the same time rate. 1st Class Mail is delivered to an address. Certified Mail is personally delivered, and requires a date/time signature of receipt. It costs more for this verification. You send 1st Class mail to those when it's good enough that it gets there.