My first GMAX model was a simple Europa XS for FS2002. Basic animations,, VERY basic texturing. Starting from absolutely no experience, it took about 3 months, working 2-3 hours EVERY day.
Since then I've modeled a Cessna 210 and Piper Cheyenne in FSDS... And then a Piper Mojave in FSDS (my first VC). Those were 6 month ordeals each.
I switched back to GMAX for my most recent creation; the FSX only, Cessna 177RG with my first, decent VC (it made it into this month's freeware cover CD on PC Pilot magazine)... That model took every bit of 500 man hours over a 9-month period... even after all my previous experience.
Currently, I'm about 50% of the way through a Cessna 310. I've been at that beast for about 4 months.

You'll find that it goes in spurts. Like for that C210. I breezed through a good chunk of the rough modeling.. but got hung up for a MONTH, trying