Excel formula into m-language

Sorry for the wrong answer.

Can you please try this query below. It seems all correct to me as per my understanding and your requirement.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("fcvRCQAgCADRVcLvhFMJylXC/deIFvDv4HH3Cq6YOh4DEmQKOzlpR2o2Hrv31f1GxurcflY9", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Created At" = _t, Tid = _t]),
    SortedRows = Table.TransformColumnTypes(Source,{{"Created At", type datetime}, {"Tid", type time}}),
    #"Added Custom" = Table.AddColumn(SortedRows, "Custom", each {null} & List.RemoveLastN( Table.Column( SortedRows, "Created At" ), 1 )),
    Custom = #"Added Custom"[Custom],
    Custom1 = Custom{0},
    ListOfLists = Table.ToColumns( SortedRows ) & { Custom1 },
    Custom2 = Table.FromColumns( 
     ListOfLists, 
     Table.ColumnNames( SortedRows ) & { "Previous Row Value" } 
            ),
    #"Changed Type1" = Table.TransformColumnTypes(Custom2,{{"Previous Row Value", type datetime}}),

    #"Added Custom2" = Table.AddColumn(#"Changed Type1", "Custom2", each {null} & List.RemoveLastN( Table.Column( #"Changed Type1", "Tid" ), 1 )),
    Custom3 = #"Added Custom2"[Custom2],
    Custom4 = Custom3{0},
    ListOfLists2 = Table.ToColumns( #"Changed Type1" ) & { Custom4 },
    Custom5 = Table.FromColumns( 
     ListOfLists2, 
     Table.ColumnNames( #"Changed Type1" ) & { "Previous Row Value2" } 
            ),
    #"Changed Type" = Table.TransformColumnTypes(Custom5,{{"Previous Row Value2", type time}}),
    #"Added Custom1" = Table.AddColumn(#"Changed Type", "Custom", each if [Created At] = [Previous Row Value] 
then
 [Tid]-[Previous Row Value2]
 else ""),
    #"Extracted Last Characters" = Table.TransformColumns(#"Added Custom1", {{"Custom", each Text.End(Text.From(_, "en-IN"), 8), type text}}),
    #"Changed Type2" = Table.TransformColumnTypes(#"Extracted Last Characters",{{"Custom", type time}}),
    #"Renamed Columns" = Table.RenameColumns(#"Changed Type2",{{"Custom", "Duration"}}),
    #"Removed Columns" = Table.RemoveColumns(#"Renamed Columns",{"Previous Row Value", "Previous Row Value2"})
in
    #"Removed Columns"

What I did?
1. Created the required table as per your data table provided in image.

2. Created 2 new columns which consists of the Previous Row Values of the Created At Column and Tid Column respectively.

3. Difference in the Tid values based upon your requirement.

4. Removing extra columns.

Thank  you.
If my answer helps you, please mark it as solution.