Even with identical aircraft... you can't say for sure how long the battery will last. Differences in how you handle the aircraft will change how long you get.

With a simple .40 size trainer, standard 4 servos, .40 LA engine, flying it at 50% throttle in smooth easy figure 8 pattern around the field, you can get over 1.5 hour of flight time from a 600 mah pack. Start running at full throttle and doing high stress aerobatics... you can cut that in half, or less.

Best advice is to do a voltage check at the end of each flight (before turning the RX off to prevent voltage rebound telling you there's more power left in the pack than what you really have...)