This one might ruffle some feathers.
Now this question could be taken a couple of ways. First, you're a career guy and was wondering how fast you can make chief [That's fine - Good for you]. Second, you're getting out after one or two enlistments, and was wondering if you could make chief before getting out. I'll address this case.
As much as I hate Khaks [and I do hate khaks], I think that it's inconsiderate to make chief at the seven-year point if you plan on getting out at the eight-year point. As I understood it, there are only so many slots and you're taking that slot from some "Lifer-Dog" first class who really loves the Navy and needs that promotion. I've never met anyone in the nuclear industry who cared whether you made chief or not. Actually I've seen a lot of resumes 86d because they made it a point to point out that they were a chief [Nobody wants to work with a guy like that - all we care about is if you can do the job, and Chief has very little to do with that].
In my own case, I was supposed to take the MMC exam at the seven-year point, but knew I was getting out and didn't sign up to take it. When he found out about it, my Senior Chief came storming down to my office ready to write me up for it. I simply explained to him that with my degrees, 4.0 evals, rankings, plant quals, ESWS and EAWS quals, along with my God-given talent for taking multiple choice tests that I was a shoe in to make E-7. Then I listed a couple dozen more-deserving MM1s on board who didn't have as much going for them, but would really appreciate making chief that year for the rest of their careers. He and the other khaks agreed that I could skip that exam and the one the following year.
In short, making chief just before you get out is just an exercise in stroking your own ego. Now I don't mind stroking my ego by qualifying on every watch station available or doing a chief's job if needed, but taking a slot that you have no intention of using just doesn't seem right to me. In that case, my ego isn't as important to me as some Lifer's career [whether I like him or not].
MGM