It depends, based on which species of Fraser salmon you're talking about.
Fraser sockeye is managed through the Fraser panel, which is the international group, predominantly. That group meets multiple times a week. I attend five or six Fraser panel meetings a week on Fraser sockeye.
Chinook is done predominantly pre-season, and then there are maybe one or two in-season changes, potentially, based on unexpected information. Predominantly, the chinook fishery is set pre-season, before the fishery starts, and then it opens as scheduled.
Obviously there can be extraneous situations, but that's generally how it works.