How long would above step take? What if btc drop significantly like 10% during this process? It doesn't seem impossible for this scenario to happen.
How long the peer-to-peer transaction will take place probably depends on what platform you're going to use. As for the withdrawal fees, it will really depend on how congested the mempool[1] will be.
But yea, it's definitely not impossible for bitcoin to move higher/lower while you're doing the transaction, but you'd have to be quite unlucky for that to happen. Unfortunately that's simply one of the risks you have to take for transferring money using bitcoin.
[1]
https://www.blockchain.com/charts/mempool-size