A nerve impulse from the brain takes one millisecond – there are 1000 milliseconds in 1 second.
With information moving that fast in order to have some traction on an automatic response pattern one needs to foster an ever evolving level of awareness – the only way to get to that level is by letting go of all “composite thinking” and to drop into presence.
Then one is aware and ready – FM was known to quote Shakespeare “The Readiness is All”
This also means a few minutes in semi-supine is worthwhile – all depends on the ability to bring awareness to the moment. In the beginning longer is spent lying down until the mind gives up under the continual will to come back to the moment. Then shorter periods are sufficient.