Calculating Non-uniform Cycle Periods

I am seeking to analyse loading cycles on a beam.

I have half hourly data for five years, in two columns A: Date and B: Load in Kg. The load on the beam is not uniform over time and shows a cycle of load.

In Column C I have an AVERAGE function that returns the average load based in the 4 hour period (2 hours backward looking and 2 hours forward looking) if it is less than 50% of the maximum load.

The data in Column C returns sets of continuous vertical cells of data showing periods of low loading and empty cells where the load is greater than 50%. The sets can be as small as one cell (i.e. one hour) to a set of contiguous vertical cells for one week of low load.

My objective is to use Excel to analyse all the sets of contiguous cells in Column C to determine the time period from the first cell of each set to the last cell of that set and drop the result into another work sheet (pivot table) to further analyse these results.