The task time estimates experienced workers provide for IPM Gantt chart development for a familiar task will be accurate "most of the time." This estimate is not an average from a task time that fluctuates broadly. It is how long the task will take, within narrow time limits, or "most of the time." For example, we can tell you with confidence that "most of the time" in summer, it will take us between 22 and 25 minutes to drive to work. We cannot ever expect to get there in under 20 minutes! Occasionally, when it rains very hard, when there is a big convention in town, or when there is an accident on the highway, we may need up to 45 minutes to get to work. It does not happen often, and 45 minutes travel time is the worst case that we have ever experienced.
When we do experience a delay, it will vary from a few minutes, which is generally caused by heavy rain, to the maximum of 20 minutes, which is caused by an accident on the highway. "Most of the time," (M), we can make it to work in 25 minutes.