Its like everything here, it depends when the expansion will stop. We now have 3 regional long haul carriers and a bunch of LoCos in the game.
Upgrades right now are taking between 3 and 4 years. But...past performance is not an indicator of future performance. Getting out my fag packet:
If you joined today it would be at 1300ish on the list. Lets assume 75 DECs/year (optimistic), after 4 years you would be behind 1600 other pilots and so to get a command we would probably need about 2900 pilots allowing for management etc. We are planning on recruiting about 250/year (I said planning!). That would be 1400/250 = 5ish years assuming the expansion keeps going at the present rate. Might be a tad quicker; might be a lot slower. As a 4000hr kind of guy you might also get screwed by accelerated commands.