How long does it take to pin on rank for O-4? I have heard after 5 years, and some say after 6 years. What about O-5? What are the requirements to do so for different branches?
Average of 6 years - just be sure to always pass your PT test, don't get arrested/do something stupid, complete an AEGD or a residency. Also, to make yourself more competitive (and possibly be promoted earlier - very hard to do this) try to deploy, go to various schools (EFMB, air assault, airborne, etc), be a brigade dentist, become board certified, stay on top of your professional military education (Captain's career course, etc)..
At least for us an AEGD or residency really isn't necessary to make O4. A specialty is much more helpful in making O5 and almost required for O6.
Yes6 years active duty?