The design and examination of time-slots using a concept originally proposed by Knott (1984) is considered with respect to work-task times having a log-normal distribution. Specific equations for this distribution are developed and a computer program to simplify calculations presented. The advantage of reducing the truncation levels so far as improving the precision and reducing the number of time-slots is demonstrated. In addition to this, the weakness of a previous, widely used, design algorithm is shown. The use of analytic and simulation approaches in evaluating time-slotting scales is explored.