Hotels in general don't allow early check-in for the general public. So since it's not a widely available option, you won't find it on search engines and web sites.
Early check-in does exist, but it is usually granted as a favor, to regular clients, members of the higher tiers of the loyalty card, etc. I was recently in Japan (where hotels are notorious to start check-ins at 13:00 or 14:00), and arrived at 6:30. By 8:00 I was at my hotel, and by 08:30 I was in bed.
Unless you have a membership with a hotel chain, forget about early check-ins. If you want to go to bed as soon as you arrive, book the hotel room from the day before your arrival, and let the hotel know you will arrive in the morning. Then you can go to bed ASAP.