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i meant the change that happens in milliseconds
I guess the following is what you heard?
Theravada abiddhamma formalizes "an experience" (thought process) in 17 discrete moments ("thought moments", cittakkhanas), or 17 cittas. An example from Abhidhammatha Sangaha ( Chap. IV - Compendium of the cognitive process):
While this is not a presentation on impermanence per se (nor it's about physical body) it's is an abbhidhamma topic that attempts to discriminate something in its detail.
It's not clear how long such a process or any of it's steps last; some say it's much much less than a millisecond.
Upvote:2
The Sattiptana Sutta says to look at Arising and Passing away of Phenomena pertaining to the 5 aggregates and 6 sense faculties. You have to experience this through what is felt, hence sensation arising and passing away pertaining to the the 4 Foundation of Mindfulness.
In the Sankhata Sutta it is mentioned that Fabrication Arise and Passes away and there appears change what exists. The change is what arises after passing away has slightly decayed from the previous cycle. Through Insight Knowledges you can get a idea of Arising and Passing away and even perhaps the decay, but generally in meditation related Suttas only mention Arising and Passing Away of Phenomena (Uppadavayadhammino) hence perhaps this level of understanding is sufficient for meditation.
Theravada Abhidhamma subdivides this atomic moment to 3 parts: uppada, thiti, vaya or uppada, thiti, banga. Other schools of Buddhism hold different version of the subdivisions that are possible for an atomic moment.
Notes From Buddhist and Pāli University for the 2nd year page 44 onwards contains more information about this as well as the interpretation in different Schools of Buddhism.
Upvote:2
This is expanded upon in SN 22.102 Aniccasaññā Sutta:
And how, monks, is the recognition of impermanence developed and cultivated so that it exhausts all passion for sensual pleasure, exhausts all passion for existence, exhausts all ignorance, exhausts and uproots all conceit of ‘I am’? ‘Such is form, such its origin, such its passing away. Such is feeling, such its origin, such its passing away. Such is recognition, such its origin, such its passing away. Such are fabrications, such their origin, such their passing away. Such is consciousness, such its origin, such its passing away.’