How long should one practice Sirshasan or Paschimottanasan or Kumbhak or Maha Mudra to awaken the Kundalini? Nothing is mentioned on this point in any book on Yoga.

It all depends upon the degree of purity, stage of evolution, the degree of purification of
the Nadis and the Pranamaya Kosha, and the degree of Vairagya and yearning for liberation.
A student starts his Sadhana from the point or stage he left in his previous birth. Some
are born with account of purity and other requisites of realization on their having undergone the
necessary discipline in their past life. They are born Siddhas. Guru Nanak, Jnana Dev of Alandi,
Vama Dev and Ashtavakra were all… http://y-v.de/dbofyI