What is the easiest way to switch between chords?
Try to keep your fingers movement at a minimum. Keep your fingers as close to the strings as possible when you're changing chords. The less you have to move your fingers, the faster you can make the switch. Practice each chord change slowly.
How long do smooth chord transitions take?
most basic chords, the changes should come in a day or two depending on how hard you practice. some fingerings i still have problems with because i may use a different fingering that feels more comfortable for me. mostly though, it all boils down to practice.