Thats not what assured access means. ULA absolutely cannot conduct a launch on 24 hours notice, nor can any launch provider. It takes months for them to prepare a launch. Payload integration alone (assuming, by some miracle, they actually had a rocket fully built, in the configuration needed, and all the development work needed to certify the combination of the rocket with a particular payload was done, and that the pad is available, exactly none of which will actually be true) takes multiple days. ULA does have, as a commercial service, RapidLaunch which is the fastest launch service in the world from order placement to liftoff, and that still takes 3 months minimum.
Assured access, as defined by the EELV program, just means there are at least 2 launch vehicles in service (in this case, Atlas V, Delta IV, and partially Falcon 9) which are capable and certified to carry the full range of national security payloads, which means problems with a single rocket design will never ground all national security payloads
Assured access, as defined by the EELV program, just means there are at least 2 launch vehicles in service (in this case, Atlas V, Delta IV, and partially Falcon 9) which are capable and certified to carry the full range of national security payloads, which means problems with a single rocket design will never ground all national security payloads