Some companies have a large stock of unique engagement rings that can be shipped virtually overnight if needed! However, if you have a more sophisticated design in mind that needs to be custom-made, they would need a minimum of 20 days to deliver the engagement ring to you. It takes at least five days to agree on the CAD design. Once they have your approval of the design, they need at least ten days to manufacture it, and another 2-5 days to deliver it to you – and again, this is a seriously rushed service we are discussing here.
The same applies to most of the industry. Since most online jewelry stores don’t have in-stock jewelry as they use drop shipping, they will need at least a week for in-stock jewelry and a month to design something customized for you.