Final answer:
The project manager should record the activity duration as 6.5 days to account for the initial 4.5-day estimate and additional buffer time for site unavailability and rain delays.
Step-by-step explanation:
The project manager should carefully consider potential delays when recording the duration for the site cleanup activity. The initial estimate of 4.5 days of schedule time assumes a full-time work week without disruptions. However, with the potential risk of site unavailability and possible rain delays, it would be prudent to include contingency time. The three workers are expected to work 40-hour weeks, which typically translates to five 8-hour days.
To account for the mentioned risk factors, the project manager could extend the duration by two days, making it 6.5 days. This would accommodate a potential one-day delay for site access and another day for rain. Therefore, if each worker is available for five full days, the project can still be completed within the extended timeframe despite disruptions, assuming no other unforeseen issues arise.