The whole idea of nuclear ICBM warfare and MAD is that you are prepared to launch at least some of your missiles before your attack capability can be removed. So, to maintain MAD capability, at least some of your missiles have to be launch capable at any time in order to effectively respond to a first strike. Of course, that readiness level can be increased if the perceived threat is higher. What that means is that a response strike needs to be able to launch in less than 30 minutes. Two hours is very generous. The first strike advantage is that you can launch most of your missiles. The MAD doctrine assures that all victories on this stage are pyrrhic.
The whole idea of nuclear ICBM warfare and MAD is that you are prepared to launch at least some of your missiles before your attack capability can be removed. So, to maintain MAD capability, at least some of your missiles have to be launch capable at any time in order to effectively respond to a first strike. Of course, that readiness level can be increased if the perceived threat is higher. What that means is that a response strike needs to be able to launch in less than 30 minutes. Two hours is very generous. The first strike advantage is that you can launch most of your missiles. The MAD doctrine assures that all victories on this stage are pyrrhic.