Our warehouse staff is fast, but even they get held up sometimes.
If an order is placed before 10 AM PST Mon-Fri it will usually ship the same day. We want our warehouse staff to be able to have a life and spend time with their families, too, though so we don't make them work over the weekend. So orders placed after 10 AM PST on Friday will not ship until Monday.
We are also closed on major holidays, and during big promotions or holiday periods the order volume can get large enough to cause delays in shipping.