Method and apparatus for statistically determining buffers for time variances for scheduled operations. Buffers for a particular operation can be based on a statistical analysis of past instances of the specific operation, and a buffer can be applied based on a selected statistical confidence interval. The statistical analysis can include determining a Gumbel distribution for time variances for a particular operation. Once buffers have been determined for the various operations, itineraries of operations can be prepared such that the scheduled times plus the buffer times for the operations in an itinerary do not exceed personnel limits of the personnel who may be assigned to the itineraries.