A no show this morning. A reshuffle this afternoon.
That empty slot is not just an hour. It is the job you turned down to keep it free.
Your diary is running you, instead of the other way round.
I look after your diary. Not a new one you have to learn, the one you already use.
I only offer slots that genuinely work, so you are not driving across town twice in a morning.
I confirm the booking, I send the reminder, and if somebody needs to move it I move it and tell you.
Most no shows happen because nobody reminded anybody. That one is a solved problem and it should not still be costing you days.
Anything I am not certain about comes to you before it goes in the diary. Your calendar is not the place for me to guess.
You are not renting software. You are putting somebody on the job who does one thing properly and does it every time.