I did FRA-PMI-AGP in January. PMI is a pretty big hub for airberlin. The airport has a bit of a weird layout but all of AB's flights leave from C gates and at most the walk between the furthest two airberlin gates would be 15 minutes. Provided everything is on time you should be comfortable with an hour connection. I had a 70 minute connection and had enough time to waste 15 minutes trying to find the lounge and then 20 minutes hanging round at the gate.