But the thing is, it's very unlikely for it to be an actual surprise attack.Someone already asked this question to Blitzo many pages ago. You can check his answer for details, but if I remember correctly, 24/7 coverage of all potential attack vectors is unrealistic. The surface area in this theater is massive.
Plus there are a whole host of other important variables involved... ECM, Decoys etc. Not only do you have to detect all the salvos, you have to have enough interceptors positioned within a crunched time limit. And even then, there's a possibility of saturation.
We're most likely gonna see tensions beforehand, so units will be on station.
Moreoever there's always spying and so on, and to ACTUALLY do such a big planned first strike, is 99.9% not gonna be something that can easily slip undetected through (the preparations and activity before it alone will alert the PLA, and units will be in heightened tension/alert).