Your `data` looks like an `EventSeries` to me. Therefore let's treat it like one.

    es = EventSeries[data /. "x" -> Missing[], 
      MissingDataMethod -> {"Interpolation", InterpolationOrder -> 0}]

    es["Path"]

>     {{978220800, 7.78}, {978307200, 5.}, {978393600, 5.}, {978480000, 5.}, {979516800, 5.}, 
     {979603200, 3.89}, {979689600, 3.89}, {979862400, 2.22}}