UTXOs are a web of forking and joining groups of sats, that have a junction based on a secret key that has the power to spend it. nothing to do with the process of mining. finding a block fixates the exact constitution of the block's transaction payload, as subjectively observed through the mempool of the miner's bitcoin node. the quantum stuff is finding the blocks. the UTXOs are just a snapshot of the flow of transactions at the location of the miner's node. UTXOs have zero relation to quantum processes except in as far as they indirectly impact the decisions and timing of action of users, which is, i guess, no less unpredictable than the finding of a block solution, but far more variance, and a practically infinite (in terms of even epochs of civilization) period before one part of the UTXOs could potentially repeat (this is related to the time to brute force a secret key). as for planck time, all we know is that matter ticks over faster the more matter is around the matter. the speed of light slows down, relative to the observer in this denser region of space, but it's kinda moot whether we could observe it because even the most well constructed sensor a) will be crushed by the pressure of matter interacting with it and b) will not be able to return any signal back to us because of the event horizon. the only thing that practically matters is how what we observe, and the signals we transmit across space, will be refracted and distorted relative to velocity and mass. so we have red and blue shifts, and we have slower and faster carrier waves to deal with, in order to tune in a signal.