ChainReactionCycles.com (CRS) ships bike parts super fast. Typical, times you may receive your order in the U.S. is 3 days. Considering they are shipping from Belfast (Ballyclare), UK, 3 days is super fast. Plan for at least 3 to 7 days, just to be safe. If you're on the west coast, it may take longer than 3 days to receive your order.
If you order something like a Custom wheelset, it will take longer since they have to build the wheels first before shipping. They use DHL, FEDEX and Parcel Force to ship packages. Bike parts typically ship out using DHL Express. Wheels will ship out using ParcelForce Global Priority.
While all orders from CRC will have to go through U.S. customs so that may slow your order down, but that's out of CRC's control. Also complete bikes or more expensive gear like frames may take longer getting through customs.
"NEW! - From March 10th 2016 if your order total is under the duty threshold of $800* (*inclusive of all shipping charges), you will not have to pay import duty."