Date Difference Not Working

I can see it is done in power query, may be best is to use dax datediff function 

Well, in Power Query you should get a result back of I believe Days:Hours:Minutes:Seconds. This all works for me here:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMtQ31DcyMLRQsLAyMAAiBUdfJR2EqCVCNFaHGNVGJKk2sTKFqI4FAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Column1 = _t, Column2 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column1", type datetime}, {"Column2", type datetime}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", each [Column2]-[Column1])
in
    #"Added Custom"

But, my stuff is all in US. Now, when this gets to DAX I end up getting values like 0.0461666666, 0.043055555, 0.450231481... which is exactly what I get if I do a ([Column2]-[Column1])*1.0 in DAX. There are ways to convert this to something useful but DATEDIFF is going to be your safest bet.