Calculate difference between the first two dates in rows using M

Hi FredPereira ,

You could refer to below M code to see whether it work or not.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMoAAJR0lQ11DXSMDBUMTKzDXzdEn2FUpVidayRACwEqMkJWEBIViqjDGbogRBICVmGA1BFmFKXZDjCEArMQMqyHIKswJG2JB0BBLLIbEAgA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [#"Case Number" = _t, #"Email Date/Time" = _t, IsIncoming = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Case Number", type text}, {"Email Date/Time", type datetime}, {"IsIncoming", type logical}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Case Number", "IsIncoming"}, {{"min", each List.Min([#"Email Date/Time"]), type datetime}}),
    #"Pivoted Column" = Table.Pivot(Table.TransformColumnTypes(#"Grouped Rows", {{"IsIncoming", type text}}, "en-US"), List.Distinct(Table.TransformColumnTypes(#"Grouped Rows", {{"IsIncoming", type text}}, "en-US")[IsIncoming]), "IsIncoming", "min"),
    #"Added Custom" = Table.AddColumn(#"Pivoted Column", "Custom", each [false]-[true]),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"false", "true"}),
    #"Merged Queries" = Table.NestedJoin(#"Removed Columns", {"Case Number"}, #"Pivoted Column", {"Case Number"}, "Removed Columns", JoinKind.LeftOuter),
    #"Expanded Removed Columns" = Table.ExpandTableColumn(#"Merged Queries", "Removed Columns", {"false", "true"}, {"false", "true"})
in
    #"Expanded Removed Columns"

Or 

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMoAAJR0lQ11DXSMDBUMTKzDXzdEn2FUpVidayRACwEqMkJWEBIViqjDGbogRBICVmGA1BFmFKXZDjCEArMQMqyHIKswJG2JB0BBLLIbEAgA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [#"Case Number" = _t, #"Email Date/Time" = _t, IsIncoming = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Case Number", type text}, {"Email Date/Time", type datetime}, {"IsIncoming", type logical}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Case Number", "IsIncoming"}, {{"min", each List.Min([#"Email Date/Time"]), type datetime}}),
    #"Pivoted Column" = Table.Pivot(Table.TransformColumnTypes(#"Grouped Rows", {{"IsIncoming", type text}}, "en-US"), List.Distinct(Table.TransformColumnTypes(#"Grouped Rows", {{"IsIncoming", type text}}, "en-US")[IsIncoming]), "IsIncoming", "min"),
    #"Added Custom" = Table.AddColumn(#"Pivoted Column", "Custom", each Duration.Days(Duration.From([false]-[true]))),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"false", "true"}),
    #"Merged Queries" = Table.NestedJoin(#"Removed Columns", {"Case Number"}, #"Changed Type", {"Case Number"}, "Removed Columns", JoinKind.LeftOuter),
    #"Expanded Removed Columns1" = Table.ExpandTableColumn(#"Merged Queries", "Removed Columns", {"Email Date/Time", "IsIncoming"}, {"Email Date/Time", "IsIncoming"}),
    #"Replaced Value" = Table.ReplaceValue(#"Expanded Removed Columns1",null,0,Replacer.ReplaceValue,{"Custom"}),
    #"Added Custom1" = Table.AddColumn(#"Replaced Value", "Custom.1", each if [Custom] <= 1 then "Y" else "N")
in
    #"Added Custom1"

Best Regards,
Zoe Zhi

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