@Kalin5 You should never allow guests to check in earlier than your stated check-in time unless the place is completely ready for them. Doing a cleaning rush job doesn't cut it.
Either set an earlier check-out time or a later check-in time, or leave a day between bookings, which really is the responsible thing to do re Covid transmission, anyway. Covid is primarily transferred through breathing in virus particles. By having one group of guests check out, the cleaner going in, and a new guest checking in 3 hours later, you are putting the incoming guests and whoever is doing the cleaning at risk. This is much more important than all the sterilizing of surfaces, much of which is largely theatre.
But of course, everything must be thoroughly cleaned. Just to give you an idea, it takes me an hour and a half to clean a small guest bedroom and a bathroom. I only host 1 guest at a time, so only one bed to make up. And that's after guests who've left it basically clean and tidy. If it's messy, it takes longer.
P.S. Giving massive discounts won't lead to better reviews. The cheaper an accommodation is, the worse the guests you are likely to get. This doesn't mean you can't get good guests with a budget-minded listing, but being ridiculously cheap isn't a good idea. I don't know how prices are in Bulgaria, but what you are charging seems awfully cheap for what you offer. $19/ night for a place that sleeps 3? That's just over $6/ person. I bet a hostel room costs more than that.