query of some time related fields

Hi experts

In pm order operation "Dates" view, there are some time fields in the screen include Earliest scheduled start time,

Earliest scheduled finish time,Latest scheduled start time,Latest scheduled finish time.

and actual start time,actual finish time.

I found the earliest and latest time were calculated automatically and they have display status,can not be changed.I want to know how system calculate and get the time?

after technical close the pm order. I found the actual time is still blank. what should I do to get the actual time and make it display in the "Dates" screen?

thanks in advance!