The two weeks applies to all of the other Exchange forums on bladeforums but there never has been a hard and fast rule here in the Flea Market. At one point people were bumping every other day but it seems to have settled back to about once a week or so. Also, IMO, if your sales post gets buried 5-6 pages deep, particularly if it's by a lot of dialogue or mung, then it's ok to bump it up. But like everything else in Fiddleback land, the rule of gentlemanly behavior applies.
Another tactic is to post your knife for sale in the Flea Market and then wait a few days and post it over in the Exchange: Custom Knives (Individual) forum. That way you can get your knife in front of eyeballs on a few different days in a few different places and bump on different schedules. Good luck!