Calculate Time

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("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", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Resource = _t, #"Created On (PST)" = _t, #"TimeStamp (PST)" = _t, Start = _t, Stop = _t, #"Booking Status" = _t, Description = _t]),
    #"Replaced Value" = Table.ReplaceValue(Source,"",null,Replacer.ReplaceValue,{"Start"}),
    #"Filled Down" = Table.FillDown(#"Replaced Value",{"Start"}),
    #"Grouped Rows" = Table.Group(#"Filled Down", {"Resource", "Start"}, {{"Stop", each List.Max([Stop]), type nullable text}}),
    #"Changed Type" = Table.TransformColumnTypes(#"Grouped Rows",{{"Start", type datetime}, {"Stop", type datetime}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Duration", each [Stop]-[Start], type duration)
in
    #"Added Custom"

How to use this code: Create a new Blank Query. Click on "Advanced Editor". Replace the code in the window with the code provided here. Click "Done". Once you examined the code, replace the Source step with your own source.