Measure a spread
A range describes these observations; it is not measurement uncertainty or a confidence interval.
Experiments
A repeatable demonstration needs a clear observation and a written account of what stayed constant.
In practice
Take several readings with the same instrument and method. Record the extremes without calling their difference a confidence interval or an estimate of every source of error.
Use suitable supervision and an established safe procedure before any practical work.
Measurements
Convert a duration
Use a consistent start and end event when comparing timed observations.