First of all, in recent years, nobody sells adventures to WotC nor Paizo, as all adventure material is developed internally. While various writers, developers and cartographers may get commissioned to do work on an adventure, those companies do not buy material developed by third parties. (I've done work for Paizo, so I know - I was one of the contributing authors to the Jade Regent Adventure Path.)
Smaller publishers also develop their own content, but will sometimes publish third party developed adventures and supplements. For example, I am the primary developer of the Kaidan setting of Japanese horror (PFRPG), which I publish as an imprint under Rite Publishing. I contacted Rite Publishing with my concept and a 1st draft version of a completed adventure. From there Steve Russell of Rite Publishing gathered some writers, developers and an editor and my setting concept has turned into a mini-adventure arc, 3 one-shot adventures and 6 supplements so far.
If memory serves it took about 3 months for me to develop, write and create maps to develop my first adventure, which was rewritten by Jonathan McAnulty of Rite Publishing once the idea was accepted. The rewrite took a further 3 months, however, 2 more adventures carrying the storyline to a true finish was written before it was finally released as a print product and PDF. Realistically, though, 3 months is a good window of time to get an adventure developed, written and edited, including doing the maps. This time frame probably varies from publisher to publisher, however.