Looking at the CO Contract of Carriage I am unable to find any reference to same day standby or of 2 hour after departure rules, so I presume that these are operational practices subject to change at the whim of the airline.

Rule 135 clearly gives the airline the right to cancel reservations of passengers who do not meet check-in time requirements.

Continental's liberal stand-by policy dates back to the days when they were in economic trouble, it sounds like they are starting to discourage passengers from avoiding higher fares.

Unfortunately you can not depend on the reservation agents for up to date knowledge of rules and operational practices.