Do not do it! The flight may be scheduled to arrive at 8:30 AM, but even if it is on time, when will you actually get to the check-in counter for the overseas flight?
I flew back from Barcelona on August 12 last year. I was in line for about an hour at the airline check-in counter alone. I made my flight, but if I hadn't gotten to the airport 3 hours ahead of time (coming from downtown Barcelona, so really no risk of significant delay), I would have been very, very nervous standing in that line.
Fly into Barcelona the afternoon before your flight home. Find a hotel not too far from the Pl. Catalunya so you can easily hop on the Aerobus the next morning. Spend the evening seeing a bit of Barcelona.