Scheduled: A Scheduled cloud flow (using the Recurrence trigger) is the most precise and scalable method for sending reminders based on a future date/time field (e.g., "2 hours before meeting"). It allows the system to query the database periodically (e.g., hourly) for records that match the time criteria. "Automated" flows trigger on data changes (Create/Update) and would require inefficient long-running "Wait" actions to handle future reminders, which is a poor architectural pattern. "Instant" flows require manual user intervention.

Outlook: The requirement involves sending a reminder email. The Microsoft 365 Outlook connector is the specific component designed to perform email actions (like "Send an email"). While the data resides in Dataverse (Contact/Appointment tables), Dataverse is the data source, not the messaging service. Microsoft Bookings is a scheduling tool; while it has internal reminders, the scenario implies a custom process flow using the specified "Contact" data, necessitating an explicit email connector.

Microsoft Learn - Run flows on a schedule: "You can create a cloud flow that triggers on a schedule... common scenarios include... scanning for data daily." (Source: learn.microsoft.com/en-us/power-automate/run-scheduled-tasks)

Microsoft Learn - Office 365 Outlook Connector: "The Office 365 Outlook connector allows you to manage your mail... Actions: Send an email (V2)." (Source: learn.microsoft.com/en-us/connectors/office365/)

Microsoft Learn - Wait conditions best practices: Documentation advises against long-running flows (waiting for days/weeks) in favor of scheduled checks for resource optimization. (Source: learn.microsoft.com/en-us/power-automate/limits-and-config)