I purchased my dress at a local bridal shop that was closing. So I purchased the dress 50% off, so there was no need to wait. So grateful, after every other store told me 6 to 8 months.
It depends on the designer, the dress, the size, any customizations, and where you get it from. Could be 2 months, could be 10. Most dresses fall in the 6-8 month mark. If you're really concerned about it, ask the place you ordered from, and they should be able to check with the designer how long it'll take.
Thanks for the responses concerning Alfred Angelo dresses. I ordered mine near the end of January, so I will continue to wait and hopefully by May my dress will be in!!!
It totally depends on where you get it and the designer. Anything from davids is always projected to be pretty quick. I got a Maggie, ordered this past Friday, and I won't see it until October at the earliest, but it could be as long as December.