This may be a bug in the function. I was experimenting with different time intervals, and I ran this with several different time increments for one day. All other parameters were the same. Below are the results showing the sum total radiation for the point over the course of the day using different time intervals:
time (hrs): WH/m2
0.1 min: 4932.670403
0.016666667 min: 2884.326145
I don't really need the 1 minute interval, but thought it should be known that it should probably not be used.
I thought it might be due to too many records in the output table - but then I tried it for only one hour, and got a much lower value for the 1 minute interval.