Unless you're defining expertise in a purely relative sense like PaulHoule here and aiming to learn something that is brand new that nobody is an expert in, I w

Unless you're defining expertise in a purely relative sense like PaulHoule here and aiming to learn something that is brand new that nobody is an expert in, I would not expect to become an expert in anything quickly. Putting aside the realism of any specific number like 10,000 hours, you can't usually just frontload that. Athletic endeavors are most obvious. You have to recover and adaptations take time besides, so simply increasing practice time density eventually becomes counterproductive. I'm sure intellectual endeavors are a bit more conducive to cramming, but not entirely. The brain is still a physical organ that requires recovery, downtime, and takes time to produce lasting adaptations.