Tough guess but...
I remember in late '99 when I started we got a brieifing on this very subject by the company & by the union....at the time upgrades were occurring around the 5 year point, plus or minus a little.
At the brief the company said it would take 7 years, the union said 9 years. I just completed my fifth full year of at SWA this month....I fully expect to upgrade to Capt sometime before my 6th yr anniversary. If hiring goes as plan, probably sometime next summer. I say all of this to caveat whatever I would propose is "expected" or "projected"....there is no way to know. Without 911, I would have upgrade probably at least a year earlier but oh well....just happy to be at SWA & doing well.
The projections from the company is we expect to double in fleet size between now & '12....that would put us at 9000 pilots since we 4500. I believe that is a bit optimisitic so lets say we go to 8000 pilots as a compromise...we will hire another 4000 pilots, expect an additional 1500 for retirements over the next 8 years, one is now talking about 5200 pilots...I would say upgrade would occur NLT than 8 years (again lots of assumptions like continued growth) but that could (& hopefully to a point much earlier) be way off.
Realize also that SWA offers upgrades to CA for the top 8% of FOs in each domiciles. They bid FO lines & then have the option to pick up CA trips & fly as a CA....this is what many folks who commute do, commute to a base that offers the earliest upgrade (again, still bidding FO lines but qualified to pick up extra CA trips). If you wish to never commute & remain in a more senior base until upgrading to CA then one's wait to upgrade will take longer...depending on the seniority of the base it may take quite a few additional years...i.e. DAL...I would never expect to be able to hold a hard line in DAL until probably 12 years with the company...too long to put off the increase in pay one receives.
Not an exact answer but the science of guessing upgrade time is art that is impossible to perfect IMHO.
Additionally, those FOs who are "lance CAs" (term we use for FOs who are qualified as CAs) can give away their FO lines & fill their schedule with nothing but available CA trips if they can. Many do this & live high on the FO seniority list but fly as CAs....a practice much debated within the lounges but a part of the contract that is helpful to those who fall into that category....have an abundance of ready to fly CAs is the company's way of "banking" CAs whenver the surge requirements for expansion exceed the training capability for new CAs...CA upgrade is around 3.5 weeks. Hope that helps,
I've attempted to be very conservative with my estimate...obviously doing the math it would appear my 8 year projection is longer than one might expect...better to have a shorter wait than a longer one is my theory.