In the US you can ship the very next day even with very busy schedules using "Carrier Pickup." @ usps.com. I don't have time to drive to post office nor to stand in line. The service is excellent!
Carrier Pickup
Key Features
Free, regardless of the number of packages you’re sending.
Your carrier will pick up your package when your regular mail is delivered.
Schedule a next day or advanced pickup up to 3 months in the future.
Available with Express Mail®, Priority Mail®, and International services.
What You Should Know:
Packages must be ready for shipment before your carrier arrives.
Requests must be received by 2:00 a.m. (CST) on the day your pickup is scheduled.
Maximum weight per package is 70 pounds.
Postage must be applied to each package.
If you are shipping postage-paid items within the United States that have been properly prepared for pickup and left in a safe location for the letter carrier, you do not need to be present. However, if you are shipping to an international destination, due to airline security regulations, you must be present at your pickup location to hand your package to your letter carrier when he arrives.
Where do I leave item(s) for Carrier Pickup?
Answer: When you fill out the online request for a free Carrier Pickup, you will be required to select the Package Location.
Possible locations may include:
In/At Mailbox
Front Door
Back Door
Side Door
Knock on Door/Ring Bell
Mail Room
Office
Reception