Vulcan's right-UA tried to impose a Sat night stay on domestic awards a few years back. But they rescinded that, maybe before it went into effect.
I never fly CO because it's impossible to use their program for oevrseas Bus1st awards. And someone said they have a 60 day clearing of upgrades for overseas-their policy says 30 days.
As for Flyer18s suggestion of acting dumb at the gate and hoping they waive the rule, well that would certainly fit with the incredible behavior I've seen at boarding gates.