I went in on a two year enlistment and made E-4 in less than a year, I was promoted in late 1972 or maybe the first month of 1973. I don’t recall it being a big deal or unusual and I was in the artillery, all these years I have felt that a racist black NCO kept me from becoming an E-5 before I got out, in fact my best friend that went in at the same time as me did make E-5 before his enlistment was up and he was a medic.
They also wanted me to go to OCS which I was fine with until it came time to go before the board that followed all the tests and I decided that it was just too much trouble and investment for someone that wasn’t going to be in long, I don’t remember if an enlistment extension was required.
At the time it was also explained by SF that if I went Special Forces I would have to extend for 8 months but I think they said that you are made an E-5 for training.
I just don’t remember the 2 year enlistment being a big hindrance to anything and definitely not a hindrance to reaching E-4.
My friend that made E-5 was also on a two year enlistment.