Hi @73project ,
If you want to implement your requirements directly through Flow, please consider referring to the following method:
- Use When a new event is created as the trigger, when the event invitation is received, Flow will trigger.
- Configure Condition to determine whether the Start Time and End Time conflict with the specified time period.
- If there is a conflict, use Respond to an event invite action to reply automatically.
It should be noted here that due to the time zone, the values displayed in Flow and Start Time /End Time set in Outlook may be inconsistent.
So we need to use addHours() function to eliminate the time difference and convert the time format.
For example, the Start Time set in Outlook is 7:30 am, and in Flow is 14:30.


So we need to use the addHours() function to subtract 7 hours before making a decision.
The parameter values configured in addHours() function are determined by the time difference of your region, or you could directly observe the time difference displayed in Flow run history and the time set in Outlook.
Expression reference:
addHours(triggerBody()?['Start'],-7,'HH:mm')
addHours(triggerBody()?['Start'],-7,'HH:mm')
addHours(triggerBody()?['End'],-7,'HH:mm')
addHours(triggerBody()?['End'],-7,'HH:mm')
Image reference:

Hope it helps.
Best Regards,