I can't be very accurate as WHM was my second job

BLM->18-WHM->30-BRD->infinty

It took me a little while back then but basically if you have the gil ahead of time to afford gear and scrolls then you can level it up very very quickly. I agree that you can do it in a few days if you have the time. If you are getting PLed to 10 then you can easily make 10-20 in under a week under normal circumstance as you will rarely be hurting for invites.

If you are gonna use it as a sub for BRD though I suggest taking it much higher. It sucks to have to change gears constantly so get it leveled up as much as you can handle before switching back to leveling your main or you'll grow to loathe it increasingly much.