I've been thinking about what annulling the order at 3:10PM means. If there is no register at Carbon Jct and no operator there, establishing a meet there would seem (as on the previous train order) to require the Farmington turn to stay there until meeting the westbound. Otherwise the westbound could never leave.
So I think that annulling the rights of 490E at 3:10PM means that (a) it cannot leave Durango unless it gets to Carbon Jct before 3:10PM and (b) if the westbound reaches Carbon Jct after 3:10PM, it does not have to wait to meet the 490E.
Bill Hobbs