In Booking.com, you can message the hotel with your question at the time you make your reservation. I'm arriving in Madrid at 8:30 am and asked the hotel for early check-in. They declined immediately, but offered to store my bag until 13:00 when I could check-in. That's what I'll do and use the time for breakfast, going to an ATM machine, buying a cell phone SIM, and finding walking poles at Decathalon...all within several blocks of each other. Catching up on sleep can wait until the afternoon