The date and time is calculated from the start date and time and the elapsed time.
Select the start date and time, input the elapsed time in days, hours, minutes, seconds, select "date and time before" or "date and time after", click the button "Calculate the Date and Time", Calculate the date and time after(before) elapsed time from the start date.
The elapsed time can be entered, such as 200 hours or 1000 minutes.