It is impossible to confirm when the accident happened, nor can it be recorded endlessly, but the information 30 minutes before the air crash is the most important information.
The black box (CVR) of the pilot voice recorder, like a tape recorder, records the voice between the pilot and passengers, hijackers and flight attendants through the speakers placed in the cockpit. It records for 30 minutes, and will start recording again after 30 minutes. So this black box records the important information in the plane 30 minutes before the air crash.