A SLBM (sub-launched ballistic missile) can reach a coastal target in less than five minutes depending on the exact trajectory. Good luck trying to intercept that.
Presumably, but the ocean is a big place. Now todays threats are far different than at the peak of the Cold War. The Russian SSBN fleet is a shell of itself, and the PLAN is still just dabbling in sub-based deterrents. The diminished threat is matched by the absolute disrepair of USN anti-sub warfare skills. These have atrophied beyond description in the last 30 years.