What is the duration of CPA course for a CA?

A CA would be able to complete the CPA course in 4 - 6 months time with enough preparation, given that there is a content overlap.

All 4 parts should be attempted. There was never any exemption of that sort. Earlier ICAI had MOU with the Colorado State Board of Accountancy. So Indian CA's could directly apply for that state board and do CPA, but sometime in 2009, the MOU was cancelled. So the advantage of just registering with