duration

It is because the right duration format should be "1.27:30:56" (note that the seperator for the day is ".")
You have have to manually bring your data in the right format (d.h:m:s)  to convert it to duration.

For example:

If you have a soruce table like this:

The code could look similar to this:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMrIyNrAyMVOK1YlWMjSyMjSxMoBwjIDCplaG5mCOibkVSBLIiQUA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Duration = _t]),
    #"Split Column by Delimiter" = Table.SplitColumn(Source,"Duration",Splitter.SplitTextByDelimiter(":", QuoteStyle.Csv),{"Duration.1", "Duration.2", "Duration.3"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Split Column by Delimiter",{{"Duration.1", Int64.Type}, {"Duration.2", Int64.Type}, {"Duration.3", Int64.Type}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Days", each Number.RoundDown([Duration.1]/24)),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Hours", each [Duration.1]-[Days]*24),
    #"Reordered Columns" = Table.ReorderColumns(#"Added Custom1",{"Duration.1", "Days", "Hours", "Duration.2", "Duration.3"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Reordered Columns",{{"Days", type text}, {"Hours", type text}, {"Duration.2", type text}, {"Duration.3", type text}}),
    #"Added Custom2" = Table.AddColumn(#"Changed Type1", "Duration Format", each [Days]&"."&[Hours]&":"&[Duration.2]&":"&[Duration.3]),
    #"Changed Type2" = Table.TransformColumnTypes(#"Added Custom2",{{"Duration Format", type duration}})
in
    #"Changed Type2"