Backwards scheduling

Hi, MMZTM load tables into PQ and try this code. 

let
    order = Excel.CurrentWorkbook(){[Name="ORDER_TABLE"]}[Content],
    operation = Excel.CurrentWorkbook(){[Name="OPERATION_TABLE"]}[Content],
    order_rec = Record.FromList(order[DELIVERY], List.Transform(order[#"Order-No."], Text.From)),
    f = (t as table) =>
        [days = List.Buffer(List.Transform(t[Time needed], (x) => Number.From(Splitter.SplitTextByDelimiter(" ")(x){0}))),
        finish = Record.Field(order_rec, Text.From(t[#"Operation-No."]{0})),
        gen = 
            List.Generate(
                () => [i = 0, d = Record.Field(order_rec, Text.From(t[#"Operation-No."]{0}))],
                (x) => days{x[i]}? <> null,
                (x) => [i = x[i] + 1, d = Date.AddDays(x[d], - days{x[i]})],
                (x) => DateTime.Date(x[d])
            ),
        out = Table.FromColumns(Table.ToColumns(t) & {gen}, Table.ColumnNames(t) & {"Completion until"})][out],
    op_gr = Table.Group(operation, {"Operation-No."}, {{"all", each f(Table.Sort(_, {"Job-No.", Order.Descending}))}}),
    z = Table.Combine(op_gr[all]),
    sorted = Table.Sort(z,{{"Operation-No.", Order.Ascending}, {"Job-No.", Order.Ascending}})
in
    sorted