How soon should you send a Abandoned Checkout Email?

It amazes me how often consumers forget to do something that us eCommerce folks want them to do. Really, we have three actions that we would love for a future customer to do:

1) Give us their email (or mobile number if outside the US)

2) Add a product to their cart

3) Checkout

Yet time and time again customers will get to points #1 & #2 but forget to do #3. Thus enters abandoned checkout emails. A great piece of automation that shoots an email to a would-be customer and reminds them to purchase what they added to their cart.

What is the best rate at which to email a customer regarding their lonely shopping cart? The results might surprise you. Looking at data from H2O Plus.

Clearly, timing plays a large factor. After three days the consumer all but forgets to come to the site and complete their purchase.