Just timed myself.

1 Minute - Still fine, no shaking, no burning
1 Minute 30 Seconds - Starting to feel the burn in forearm and release shoulder
1 Minute 45 Seconds - Still feeling the burn, starting to shake
2 Minutes 3 Seconds- Let down

I could have held longer if I absolutely had to. Mind you this is while holding on a target at 20 yards.

62lbs, 65% letoff.