In Magento 1.x, enabling Saturday delivery via UPS is not a default function. For that reason, this simple extension will allow for adding Saturday UPS shipping methods.
System -> Configuration -> Shipping Settings -> Saturday Delivery - UPS
System -> Configuration -> Shipping Methods -> UPS
The UPS API considers Saturday Delivery to be a shipping option, not a different rate. For that reason this module will make two requests to the UPS API - once for non-Satuday rates and a second request for Saturday rates. Magento will then merge these two requests into one rate block for UPS.
Developed and tested on Magento Enterprise Edition 1.14.2.0