I have never attended or even looked up competition rules and examples however I would guess that it would be a lot of different distances and nothing set in stone. I would bet a max distance would be up to 20 + yards.
For several years the U.S., France and some in Japan all shot ten meters. The exception was the JSFA in Japan with several thousand members paying to compete. They had shorter distances for less experienced shooters. France has also had shorter distances for quite some time. I established the USBA about three years ago to give Americans the shorter range options as well as to remove some restrictions that had been in effect for IFA sanctioned competitions.
A few years ago the German national blowgun club (DBSC) decided on multiple competition classifications with distances of seven, ten and fifteen meters. They also allow blowguns up to six feet in length (perhaps longer?) while all the others I have mentioned limit competition tube lengths to four feet (120cm.)
The annual blowgun competition that is part of the Cherokee Nation Holiday celebration in Talequah Oklahoma has had the men shooting about forty=five feet the last three or four years and closer to thirty feet for the women and kids. Rivercane blowguns only for that one.