According to Sheri Williamson's "Hummingbirds of North America", black chins start arriving in the US around March 1 and make it to Oregon between April 21 and May 1. So that's 6 to 8 weeks for the US portion of the journey. It takes time to replenish their fat reserves at the interim stops, and they also have to time it so they arrive when the flowers are blooming at their destination.
Black chins winter in the middle section of Mexico's Pacific coast so it looks like the Mexican portion of the journey is about the same distance as the trip from the border to Oregon. I don't have any information on how much time they spend on this part of the trip.