
Three minutes is a common length for typing tests at school and in job applications. Type a random passage for three minutes and get your words per minute and accuracy as soon as time is up.
It's long enough that you can't coast on a burst of speed, but short enough to stay focused the whole way through. That's why many typing classes and employers use tests of around three to five minutes when they want a realistic number.
Start at a pace you can hold instead of sprinting, speed that collapses after the first minute costs more than it gains. Keep your eyes on the text, correct mistakes quickly and keep going, and don't stop to check the timer.
Most people can hold their concentration for a minute without trying. By the third minute attention drifts, shoulders tighten and small errors creep in. That is exactly why this length is useful: it shows whether your technique holds once the easy start is over. If your accuracy falls in the last minute, the fix is usually posture and breathing, not faster fingers.
Take one test and note your WPM and accuracy. Then spend five minutes on slow, careful typing of whichever keys or letter pairs tripped you up. Finish with a second test. Done three or four times a week, this small loop of test, fix and retest moves your score more reliably than repeating the test over and over.