Hi
@ayenco,
You can't. Options are you can only clear all hour or reset to default.
However what you can do is kind of merge two together. In other words where you had one covering a specific time, use two - for example, whereas I used one slot for Monday 08:00 - 18:00 previously I would now use Monday 08:00 - 14:00 and 15:00 - 18:00, so the slot is made use of without having to change anything else.
However, me being me I would probably take a screenshot, reset and re-do it then save the changes.
I think this should be a feature so I have raised the feedback item for you here:
https://feedbackportal.microsoft.com/feedback/idea/ae6eb700-1061-ec11-a819-6045bd7c3bc6Hope that answers your question!
Best, Chris
Best, Chris