Dear DanielaQB,
Good day! Thank you for posting to Microsoft Community. We are happy to assist you.
In order to understand your query and provide possible solution, May I please double confirm if you want to create a service for specific date and specific time? if so, May I please confirm if you tried to create a service with "Set Different availability for a date range" option? if not, kindly follow the steps below and check if there is any difference. To do this, Sign in to your Microsoft Bookings -->Services -->Add new service -->Add your basic Details --> Availability option, under General availability, Select Not Bookable -->Click on "Set Different availability for date range" -->Select start and end date -->Select Custom Hour to specify the date and time as your time requirement. You can refer to the Example screenshot below.
Let's say you want to schedule meeting with customer on 19-Nov-2023 from 11:00am to 5:00pm. Therefore, set the general availability as not bookable and select start and end date as 19-11-2023. Then, select custom hour option to set specific time. check the exact date and adjust your time. If you want to schedule for other additional day, may be for 21-11-2023, Select "Set different availability for date range" and set 21 as start and end date and follow the same step.

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The test result for the above schedule is as below:

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If you are referring for different scenario, could you please clarify? I will test from my side and provide you with possible solutions.
I look forward to your update. Please feel free to let me know how it goes or if I got you wrong. If you still have any concerns, please let me know so I can provide more suggestions.
Thank you for your precious time. Have a nice day.
Sincerely,
Libeamlak | Microsoft Community Moderator