We like to re-calibrate the gyro bias as close to the start of the match as possible. MEMS devices are highly sensitive to temperature and they self-heat as they draw current, so in the couple minutes between when you turn your robot on and when the match starts, your zero may have drifted a bit. It still isn’t perfect, but it will be better than calibrating a cold gyro.
One automated way to do a reset that is commonly used in industry is a “zero velocity update” - if you know (via another source, such as wheel encoders or a button press) that your heading should not be changing, you can re-calibrate the bias on the fly and recover some of the accumulated heading error.