How is a "Power to KWh" feed calculated? and how does the "fixed interval" work?

part 1) As power readings are received, how are these converted to KWh? To integrate the KWh value, where does the TIME value come in? Is the “fixed interval” time used? Or does it take the delta T from the previous value entered?

part 2) The documentation says feed “fixed interval” times should be set to equal or greater than the time expected for data values to be received ( so as to not use up too much memory). So, what do these times do in the calculations if they can be set to values GREATER than the expected send intervals? If its too much larger - say data is sent every ± 10 secs, and th “fixed interval” is set to 60secs, how will it affect the results?