You can always tell just exactly how long anything takes.
Tap on the Start button.
You can swipe left on the stopwatch to reveal an analog-style stopwatch if you prefer.
Tap on the Stop button.
Now your Stopwatch is stopped. You can easily resume the stopwatch from where you stopped it by once again hitting the Start button.
Tap on the Lap button.
The stopwatch will continue to run and now you have marked a lap time. The lap time will appear below the running timer.