There's a variable trip curve that varies from breaker to breaker. It's a pretty big window since the devices are so simple, and variations in manufacture, ambient temperature, etc, impact the actual trip point. Long-time trip is usually something like 1.0-1.4x with larger tolerances for shorter trips. 5 minutes put it somewhere around 1.4-2.0x current.
Bottom line is that these breakers should NOT be tripping in 5 minutes at 83% the breaker rating.
