Time to allow for train from Apelonia station to orient station
I suggest you allow just enough time.
if you mean changing trains at Oriente I suggest minimum 5 minutes, be very comfortable with 10.
At Oriente you must go down from the platform to the mezzanine for the departures screens, spot the platform indication for your next train, then find your way back up to the correct platform.
It takes 9 or 10 minutes from Santa Apolónia to Oriente. Trains are irregular, especially at weekends, so do check those times carefully.