Understanding Machine Utilization based on On and Off Times

I worked with the data in Excel, but you can have your data in any source.  Just change the Source line to whatever your actual source is.

For Part 1, I assumed each row represents a different machine, and that the times off and on do not extend past midnight.

You can then use a combination of List.Generate and List.Accumulate to break down the number of minutes in each segment:

let

//change next line to reflect actual data source
    Source = Excel.CurrentWorkbook(){[Name="Table11"]}[Content],

//create list of all time segments
    #"Time Segments" = List.Buffer(List.Times(#time(0,0,0), 96, #duration(0,0,15,0))),
    colHeaders = List.Transform(#"Time Segments", each Time.ToText(_,"HHmm-") & Time.ToText(_+#duration(0,0,15,0),"HHmm")),

//set data types
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Machine", type text}, {"On", type time}, {"Off", type time}}),

//create Lists of all the durations for each row
    Durations = List.Generate(
        ()=>[m=List.Accumulate(
                    #"Time Segments",
                    {}, (state, current)=>
                    state & {List.Max({0,Duration.Minutes(List.Min({#"Changed Type"[Off]{0}, current + #duration(0,0,15,0)}) - 
                    List.Max({#"Changed Type"[On]{0},current}))})}),
                    idx=0],
            each [idx] < Table.RowCount(#"Changed Type"),
            each [m=List.Accumulate(
                    #"Time Segments",
                    {}, (state, current)=>
                    state & {List.Max({0,Duration.Minutes(List.Min({#"Changed Type"[Off]{[idx]+1}, current}) - 
                    List.Max({#"Changed Type"[On]{[idx]+1},current - #duration(0,0,15,0)}))})}),
                    idx=[idx]+1],
            each [m]),

//create new table,
    #"Duration Records" = List.Transform(Durations, each Record.FromList(_, colHeaders)),
    newTable = Table.FromColumns(
        Table.ToColumns(#"Changed Type") & {#"Duration Records"},
        type table[Machine=text, On=time, Off=time, Results=record]
    ),
    #"Expanded Results" = Table.ExpandRecordColumn(newTable, "Results", colHeaders),
    #"Type new Columns" = Table.TransformColumnTypes(#"Expanded Results", List.Transform(colHeaders, each {_, Int64.Type}))
in
    #"Type new Columns"

Results