Slow IF statements when converting a single cell to a column value for multiple files

[dispelthemyth]

I am importing multiple small files (8 files ~ 800 rows total) and have 3 values

Values i want are in row 1, 2 and 4 of the Trial Balance column in all 8 files but obviously when combined will be in rows 1, 2, 4 then maybe 104, 105 and 107

I am currently doing 3 separate If statements via adding a column

As the 2nd one always starts "As at" i use that to find all 3 values i need

= Table.AddColumn(#"Added Index", "Division", each if Text.Start(#"Added Index" [Trial Balance] {[Index]}, 5) = "As at" then #"Added Index" [Trial Balance] {[Index] -1} else null)

= Table.AddColumn(#"Added Division Temp", "Date", each if Text.Start(#"Added Division Temp" [Trial Balance] {[Index]}, 5) = "As at" then #"Added Division Temp" [Trial Balance] {[Index]} else null)

= Table.AddColumn(#"Added Date Temp", "Sub Division", each if #"Added Date Temp" [Date]{[Index]} = null then null else #"Added Date Temp" [Trial Balance]{[Index] + 2})

These If statements (any of them) make the query very slow to run, like 2+ minutes, which becomes unusable one i get 12 months of data (48 files)

Are there any better techniques for converting specific cells to a column label for multiple files?
Are If statements inherently slow in PQ or is mine just poorly written?

let
    Source = #"TBs Import location",
    #"Filtered Hidden Files1" = Table.SelectRows(Source, each [Attributes]?[Hidden]? <> true),
    #"Invoke Custom Function1" = Table.AddColumn(#"Filtered Hidden Files1", "Transform File", each #"Transform File"([Content])),
    Renamed_Columns = Table.RenameColumns(#"Invoke Custom Function1", {"Name", "Source.Name"}),
    #"Removed Other Columns1" = Table.SelectColumns(Renamed_Columns, {"Source.Name", "Transform File"}),
    #"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File", Table.ColumnNames(#"Transform File"(#"Sample File"))),
    #"Changed Type" = Table.TransformColumnTypes(#"Expanded Table Column1",{{"Source.Name", type text}, {"Trial Balance", type text}, {"Column2", type text}, {"Column3", type any}, {"Column4", type any}}),
    #"Replaced Value3" = Table.ReplaceValue(#"Changed Type","Company Name","Test Entity Name",Replacer.ReplaceText,{"Trial Balance"}),
    #"Added Index" = Table.AddIndexColumn(#"Replaced Value3", "Index", 0, 1, Int64.Type),
    #"Added Division Temp" = Table.AddColumn(#"Added Index", "Division", each if Text.Start(#"Added Index" [Trial Balance] {[Index]}, 5) = "As at" then #"Added Index" [Trial Balance] {[Index] -1} else null),
    #"Added Date Temp" = Table.AddColumn(#"Added Division Temp", "Date", each if Text.Start(#"Added Division Temp" [Trial Balance] {[Index]}, 5) = "As at" then #"Added Division Temp" [Trial Balance] {[Index]} else null),
    #"Added Custom" = Table.AddColumn(#"Added Date Temp", "Sub Division", each if #"Added Date Temp" [Date]{[Index]} = null then null else #"Added Date Temp" [Trial Balance]{[Index] + 2}),
    #"Filled Down" = Table.FillDown(#"Added Custom",{"Division", "Date", "Sub Division"}),
    #"Removed Columns" = Table.RemoveColumns(#"Filled Down",{"Source.Name"})
in
    #"Removed Columns"

 

[dispelthemyth]

EDIT: TIL you can get a query called "Transform Sample File" created which you can amend to change all imported files before it hits your main query