Is There a Delay in Detecting an Incoming Missile?

The chinese tested a so called fractional orbital bombardment system that also used a hypersonic glide vehicle. These systems were put into very limited use by the soviets in the 19 sixties. Now, because we have the ability to guide weapons with much greater precision, theoretically it is possible to use hypersonic bustlide weapons which could be more accurate and potentially need lower altitudes. But I don't personally think hyposonic weapons are going to become central to china's nucler deterrent even if they are used to some extent.