Comlex I, II, & III are required in order to get licensed to practice medicine. You take Step III after the intern year of residency. It is required in order to graduate from residency and you need to pass it in order to be able to sit for the residency board exams. When you pass the board exam then you are board certfied.
Timeline:
Med School: Yr 1, Yr 2, Comlex I, Yr 3, Comlex IICE/PE (2 parts) during 4th yr
Residency: Yr 1, Comlex III Yr 2-6 (depending on specialty) When you pass then you can apply for a license to practice and can moonlight during residency. Need to pass in order to graduate from residency.
Take Board Exam, Graduate Residency