In my experience, the best way to ensure fastest shipping (assuming you're using standard/ground shipping) is to order on a Saturday night/Sunday morning. This makes it so that when business hours begin on Monday, yours is among the first orders waiting to processed, which usually means it'll ship later that same day. Then it has all five working days uninterrupted to reach you.
If you order late in the week, your order might go out same day, but since the mail grinds to a halt on Sunday (or the entire weekend via UPS/FedEx/etc), you get an extra day or two tacked on to your shipping time.