A medium to full trance state is needed.

Trance states (same as altered states, just different terms) relate to sleep. Humans have on average a 90 minute sleep cycle, starting with light sleep (light trance) and moving through a range into deep dreamless sleep (full or heavy trance state)

https://en.wikipedia.org/wiki/Sleep

Now, you may be able to enter a fairly deep level in a short period of time, but you cannot really get around nature, and the full 90 to 110 minute cycle should be worked with.

The full trance state has been found to be the best level for OBE and other psychic type phenomena. It is as if all the Chakras open during the deepest stage of sleep/trance.

This is why long sessions are recommended, so you can take advantage of the deeper levels for raising Kundalini.

robert