This meditation is a meeting between you and the cosmos, between you and the whole of existence. It helps you to merge, melt and let-go on the deepest level possible.
There are two stages, with no precise timing for each. The format given below is one that works well to start with. You can do this meditation any time during the day or just before you go to sleep. If you choose to do it during the day, make sure you have some free time afterward before resuming your normal activities.

The meditation can be done with its specific OSHO Mahamudra Meditation music, which indicates and energetically supports the different stages.
For the music availability, see below. 

Instructions:
The meditation lasts 50 minutes and has two stages.

First Stage: 30 minutes
Stand with closed eyes, allowing your body to be loose and receptive, waiting, and then cooperating when you suddenly feel an urge for your body to start moving. When your body is relaxed and allowing, subtle energies that are outside your control begin to move it. Let your highest possibility take possession of your body and do this. Just allow it to happen. This is Latihan. And witnessing has to be joined to it, remain a witness.

Second Stage: 20 minutes
Kneeling down, eyes closed, raise both hands toward the sky, palms upward. Feel yourself to be like a hollow bamboo or a pot. Your head is the mouth of an empty pot and tremendous energy is falling onto your head. Nothing but emptiness inside, the energy is filling you completely. Let it go as deeply as possible into your body, mind, and soul. Your body will start trembling and shaking, like a leaf in a strong wind.
When you feel filled, the energy overflowing, bend forward. Rest your forehead on the ground. Now pour the energy down into the earth. You take from the sky and give back to the earth. Just be a hollow bamboo in between, passing the energy.
Then raise your hands again, fill again, pour down again. Do it at least seven times. Each time it penetrates one chakra, one center of the body, and goes deeper. You can do more, but not less.
And this will be a complete Mahamudra.

Note:
For full details about this meditation, see: Tantra: The Supreme Understanding, #6, by Osho

Osho explains about this meditation:
“If you do this every day, soon, somewhere within three months, one day you will feel you are not there. Just the energy is pulsating with the universe – nobody is there, the ego is completely lost, the doer is not. The universe is there, and you are there, the wave pulsating with the ocean – that is Mahamudra. That is the final orgasm, the most blissful state of consciousness that is possible.”

You can participate in this and other OSHO meditations online here.

You can download the music for this meditation here.
The music is also available with a Spotify, Apple Music, and Prime Music subscription.