"Timeless awareness" is a translator's gloss of the term ye shes. You cannot understand Dzogchen without understand the terms and a bit of tibetan grammer. These are the various ways this term has been translated:
ye shes - jnana, (exalted, primordial) wisdom, (primal, transcending, original, unitary, authentic, pure, absolute, a priori, genuine, spiritual, ever-fresh, pristine) awareness, wakefulness, pristine cognition, mystic illumination, gnosis, understanding by peak experience, (intuitive, transcending, comprehensive, true) knowledge, SA mched pa'i ye shes, mnyam nyid ye shes, me long ye shes, chos dbyings ye shes, bya sgrub ye shes, sor rtog ye shes, perfect absolute divine wisdom, pristine wisdom, primordial awareness, timeless awareness
Since the brain is made of five elements, it too is made of the five wisdoms (ye shes) of vidyā. Therefore, there is no problem with awareness, etc., having a basis in the body. Actually, what we say in Dzogchen is that the wisdom of vidyā is located in the heart, the energy of vidyā is located in the brain, where it governs sense organs and cognitions.
Thanks Malcolm very useful. I understand the 'ever-fresh' aspect to it in the sense that it's so fresh that it seems unborn, but in what way can ye she be said to come into existence? I mean if ye shes is indeterminate or ever-fresh then in what sense are the elements 'formed'? What accounts for perceived 'duration' of the elements'?