In short, you're fine. There's no time table for MS degrees, especially when you are working full time. You can't complete a Master's degree in ANY amount of time if you are not "serious" about school, so don't worry. B-schools expect to see lower grades from engineering schools because it's widely known that they do not practice grade inflation, and that the degree is really tough. Plus, the more time you are out, the less it matters. With a 740 GMAT, an engineering degree, progressively responsible career experience and well written essays, you should have a fairly easy run at your list of schools. Good luck.