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(Not speaking for the actual expert) - I think I read that missiles require two separate Launch Control Facilities (LCF) to turn keys for immediate launch, but will eventually launch after a (classified) delay if just one does (unless vetoed by other LCFs in the same group).

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This is roughly correct. In addition to the immediate ground launch crew votes (in reality a squadron is 5 launch centers, i.e. capsules, all interconnected to a total of 50 missiles, and as stated two launch control centers need to successfully “vote”), there is always an airborne launch control center flying over ready to provide a second vote after a specific time-out period. In fact one of our primary nuclear safety and control concerns was to keep refreshing the ALCC access timer.

Thanks. I did wonder what the launch veto system was actually for? - working from the assumption that it would be procedurally impossible for a crew to successfully vote for a launch without receiving the correct authorisation codes from an external source first. (I guess it suggested to me that a rogue launch could technically happen, but given any system can go wrong (machinery or operators) perhaps it just made sense to have as many inhibitory safety systems as possible).

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