How to Calculate Time difference from a single column

In Power Query (Transform Data), you can

• you don't need the Index column
• if Date column not sorted ascending, then do so
• Add a "shifted date column" where the dates are shifted down one
• Subtract the "shifted column" from the date column
• Remove the "shifted column"

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCk9N0VEwMFTwTSxSMDIwMlYwMLcyMLAyNVaK1cEha2hlaIRP1givXmMD3LLmeGUtwbKxAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type datetime}}),
    
    #"Add Shifted Date Column" = 
        Table.FromColumns(
            Table.ToColumns(#"Changed Type") & 
            {{null} & List.RemoveLastN(#"Changed Type"[Date],1)},
            type table[Date=datetime, Shifted Date=nullable datetime]),
    
    #"Add Time Difference Column" = Table.AddColumn(#"Add Shifted Date Column", "Time Difference", 
            each [Date] - [Shifted Date], type duration),
            
    #"Remove Shifted Date Column" = Table.RemoveColumns(#"Add Time Difference Column",{"Shifted Date"})
in
    #"Remove Shifted Date Column"

You could also do this with DAX, using a similar algorithm.

Again, the below assumes the DATE column is sorted ascending.

You select to add a column, with this DAX formula:

Time Diff = var SHIFT = OFFSET(-1,ALL('Table'[Date]))
            return if(SHIFT=0,BLANK(),'Table'[Date] - SHIFT)