Hi, Alex 

Thanks for reaching out to us

If you wish to create a specific working hour schedule for a certain day, 

but to have "regular schedule" on other days,

you can try to create a "special day" for the employee.

Here is my example - if i have regular work hours like this :

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if we want to "make him unavailable" from 12 until 15 hours;  but available for the rest of the shift;

i add a special day,  and this will override the work hours for that day only :

Then if someone tries to book on that day,  the customers will only see the available time slots for the time you set here.

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You can see more about Special Days in Amelia here.

Let us know if that works as a solution? Thank you