The uncertainties (e.g. altering labor productivity, weather changes, material shipment delays, and site-based conditions) have been the root causes of the construction industry continuously struggling to perfectly estimate the durations of activities, which are expected to be properly planned, scheduled, and will thereby control the cost of a project. Conventional approaches that involve probabilistic assessments such as Critical Path Method (CPM) and Program Evaluation and review techniques (PERT) use fixed or constrained probabilistic estimations, and frequently do not consider the range of expert opinion or arrive at a consensus of uncertain time parameters. This paper will utilize a Delphi method that is a systematic, iterative process used to elicit and hone the views of the experts to come up with a collaborative approach to estimating the time taken by construction activities. The tasks are as follows: to carry out a Delphi survey of the experienced construction professionals in a series of rounds and reach the consensus on the likely ranges of project activity durations, and also test the technique by using a case study of a building construction project. Three surveys of anonymous panel of 12 experts (with more than 10 years of experience) were implemented, including the open-ended estimates, statistical feedback and revisions until the consensus was achieved (coefficient of variation was less than 15 per cent). The estimated duration based on the case study outcomes was refined down to 7 days to 13 days during foundation excavations (median: 10 days) and labor availability was used as the reason (35% weight). The Delphi method also proved more accurate since it yielded tighter ranges and smaller variance of schedules by 15 percent compared to PERT in the case study. Several factors combine in this research to give an easy-to-use and consensus-based method of duration estimation, and consequently improving risk management and schedule accuracy. It provides construction managers practical knowledge to make informed decisions regarding resource planning, facilitates the union with digital planning software, and encourages efficiency within an ecosystem where delays occur in more than 70 percent of projects creating resilient and sustainable project execution.
