Adjusting the Estimated Delivery Date Range

[readybuyer]

Hi everyone. I've got a package that I can ship using the new USPS First Class Mail "up to 15.999 ounces" method. When the item was sold, it was set up for Priority Mail because the package weighed more than 13 ounces.

If the buyer elects to ship the package via First Class Mail, will eBay adjust the "Estimated Delivery" window on the sale? I could offer the customer a $3.00 refund and ship First Class, but I don't want eBay to hit me with a defect because I missed the original delivery window trying to offer the buyer good service.

Thanks!