I could be wrong (as I don’t use that function), but I think it will record as long as there is available internal memory space. You cannot record to an external SD card. Remember it records in .wav format, not .mp3 so it will probably take up more space than you think.
The question is, will the sound quality of the recording be of a high enough value that you would want to listen to the playback afterwards? Having the teeny-tiny micro-mic and the unit in your pocket, I think all it’s going to pick up is your clothes rustling as you move, and people around you whispering and coughing.
The voice recording feature is handy for ‘jotting down’ little reminders or notes to yourself (like a grocery list, driving directions or remembering to call someone later), or recording a meeting or interview with someone and maybe for recording lectures, but a concert? I doubt it would be worth the time.