Airport arrival time outgoing regional flight

Two hours prior to your flight’s departure time.

It also depends on what time the check in desk opens and security opens.

the safe answer is whatever time the airline says because if some random stranger on the internet tells you wrong you wil have no comeback. It will depend on whether you have checked baggage and whether you have checked in online.

Don't forget that Madrid and Porto are in different time zones, the flight is 75 minutes.

Madrid’s airport (MAD) is open 24/7. Security is open around the clock as well. Check-in counters for Schengen zone flights open at least two hours prior to departure.