Date / Time difference excluding weekends and factoring working hours

so complicated...

(from, to, optional st, optional et) => 
    [s_time = st ?? #time(8, 0, 0), 
    e_time = et ?? #time(17, 0, 0),
    start = List.Min({from, to}),
    end = List.Max({from, to}),
    start_date = Date.From(start),
    end_date = Date.From(end),
    gen = List.Generate(
        () => [c = start_date, sod = List.Max({start, start_date & s_time}), eod = List.Min({end, c & e_time})], 
        (x) => x[c] <= end_date, 
        (x) => [c = Date.AddDays(x[c], 1), sod = c & s_time, eod = List.Min({end, c & e_time})],
        (x) => if Date.DayOfWeek(x[c], Day.Monday) > 4 then null else x[eod] - x[sod]
    ), 
    result = if List.NonNullCount({from, to}) < 2 then null else List.Sum(gen)][result]