Hi Mike,
A customer service schedule determines the business hours for each day in a week and also the weekly off. Customer Service uses these details for time tracking of service-level agreements (SLAs).
However, sla can’t send email alert when case is created out of business hours, it just can extend the countdown.
So you have to compare created on field value with business hours directly, the flow maybe one way, but it just can check specific date is a weekday by using the dayOfWeek function.
which returns a number – 0 is Sunday, 6 is Saturday, and anything in between is a weekday.
For example:

For time of the date field, it’s hard to compare,i have not found a way to compare time.
So you have to check created on field of the case manually to specify whether the case was created during or outside business hours.
Regards,
Leah Ju
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