USB, unlike say single ended audio, is a tightly specified standard with a non-profit corporation -- USB Implementers Forum, Inc. -- that maintains standards. The standard for USB 2.0, which I think is still what most DACs are using, is a 680 page document with extensive mechanical and electrical specs for cabling, with length maximums determined by signal pair attenuation and propagation delay for each class of USB speed to ensure interoperability and signal integrity. The spec for USB 2.0 for full and high speed data is max cable length of 5 meters, I think.
No doubt there are poorly made and poorly shielded USB cables in the market at one end, but even ad the audiophile end, I'm not sure how many if any audiophile USB cable sellers go for USIF compliance certification. But a USB cable at the OP's proposed lengths -- 1 foot vs. 3 feet -- the differences in length should make no difference if the cable is property shielded and meets spec.
