Depends on how the hiring is going, of course. For someone who started 5 years ago, it took less than a year and a half. For someone who started a year later, it took nearly 3 years because of our furloughs in August 2001. Then the floodgates opened with our expansion into Cleveland, and the folks we hired this past January (many CoEx furloughees included) upgraded in about 8 months. But that was during a big expansion, which I don't foresee happening again anytime soon.
To say "it varies widely" is an understatement. With the next new-hire class only 2/3 the size of a normal one (8 vs 12 people), I'd say things are stagnating again, so it's anybody's guess. I think future upgrades will be driven by people leaving at this point, and not many are right now. I'd plan on at least a couple years.