Program Duration

The minimum time would be using the early dates

The maximum time would be using the late dates

for the minimum durations you can make them equal to the schedule which is being done on time

for the maximum duration you can use the schedule where it is not being done on time 

for the most likely durations you can use the value between the max and the min durations 

Nifemi;

I don't understand your situation - critical schedule and normal schedule to be merged.

Absent analysis, I propose you modify the durations by a percentage. PRA defaults to +/-25%, which may or may not be applicable. Assuming the current durations came from a credible estimate, those durations are your most likely. The optimistic is the likely times -%, I'd go with 10%. So your optimistic would be .9 likely. Similarly for the pessimistic. I'd suggest 25%, so it would be 1.25 likely. Then use the deterministic (calculated) dates for each of the three runs.

This is not the way it should be done. This method does not allow for variability (stochasitic variability) within the range. My caution is not to do this. You won't get the 'answer' you seek. Your program appears to violate sound project control methodologies. Please re-think.