@Quincy I hope you are doing well!
I have a key box that I hang on the entrance doorknob. This gives the option for my guests to do self-check-in when I am not home. I always send a check-in instruction one day before their arrival. It is very thorough with the address, self-check-in instruction (how to get the key out, where is the key box little door, etc), parking information, once they are in the house where to go to find their room and also for the bathroom. My check-in time is anytime after 3pm. I rarely take an early check-in because fortunately, my place is pretty booked (so, there are many back to back reservations). I do not have the limit time for check-in, I have had guests who checked in at 2am (and they paid for the night before). However, I have a house silent time in my house rules (10pm-7am), so guests who need to do late check-in are expected to keep the noise down during the house silent time. For guests who are coming in late, I usually see them and give the house tour in the following morning.
For check-out, I always send a check-out instruction the night before check-out or on the morning of at the latest. Guests can check-out anytime before 11am. I definitely like guests who check-out early, it gives me more time to prepare the room for the next guests. However, not too early that they need to make a lot of noise in early morning.... ha ha (in the perfect world)
Check-out instruction has a thorough information (turn off heater and lights, put the dirty towel on the floor, lock the front door, put the key back in the key box and "mix" the code).
If I am home and up when they arrive/about to leave, I usually get the key for and from them to save their time from putting it from/back to the key box.