@Danny627.Welcome to hosting 🙂
My Schlage Encode smartlock not only issues codes but access times down to the minute. If they turn up early they wont get early access unless they contact me and I approve a change. The code message they receive clearly sets out the access times and dates as well.
I usually issue codes first thing in the morning of a stay, sometimes the night before if early entry is approved. This information is also in the Airbnb arrival guest info.
You will find a lot of helpful advice from other hosts on Community Centre so spend some time reading and searching topics.
Good luck.