In a normal season (are you tired of hearing that yet?) the Canadian Hockey League — aka the CHL, aka the OHL, QMJHL and WHL — start their seasons right about the same time as the NHL and AHL. All of this is timed out to allow for the transfer of players from the NHL to the AHL in time for their training camp and opening night and also to the CHL teams.
Because that timing has only seriously been challenged by NHL lockouts, the agreements that govern how players move in and out of the NHL are written with some unwritten assumptions.