I bought a Lycoming rebuilt (zero-time) IO360 in November, 2020. It was delivered in February, 2021 (after the delivery date slipped about a month in several installments). I had my engine off the mount long before the new one was delivered, and all of the accessories (oil cooler, prop governor) were back from overhaul. So reinstallation after the engine arrived took about 5 days (I did the labor with my A&P/IA supervising). I had considered keeping the old core and rebuilding it myself with my A&P, then pickling it and keeping it as a ready spare, but the $17,500 core charge disabused me of that notion. If they had charged only $5-7,000, I would have probably done it.