Your examples are of the DateTime type, NOT DateTimeZone. Accordingly, the below code for a Power Query function uses DateTime. You should be able to adapt it to your actual problem
Also, the code is more generalized and includes an optional Holidays list. You can create the list yourself, which, if you have thousands of dates, would be more efficient, as the code will download an appropriate list each time it executes.
//Note optional Holidays parameter
//You can substitute a self-generated List of holidays, or use the website in the code to download a list
// If you use the website, be sure to use a recognized country abbreviation
//If you are using holidays, you should separate this list and buffer the result for speed issues.
// as written, it will download this list every time the function executes
(start as datetime, numDays as number, optional Country as nullable text) =>
let
adjNumDays = Number.RoundAwayFromZero(Number.Abs(numDays*7/5))*2,
yrStart = Date.Year(start),
yrEnd = Date.Year(Date.AddDays(start,adjNumDays*Number.Sign(numDays))),
//Create list of country specific Holidays
yrs = {List.Min({yrEnd,yrStart})..List.Max({yrEnd,yrStart})},
holidays = if Country = null then {} else
List.Accumulate(yrs,{},(state,current) =>
let
Source=Web.Page(Web.Contents("https://www.officeholidays.com/countries/" & Country & "/" & Number.ToText(current))),
Data0 = Source{0}[Data],
DateCol = Table.SelectColumns(Data0,"Date"),
fullDate = List.Transform(DateCol[Date], each Date.FromText(_ & " " & Number.ToText(current)))
in
state & fullDate),
//all Working dates
//Generates a list of working dates in either Ascending or Descending order
// based on the Sign of numDays
// starting with the first working date after Start
allWorkDates =
List.RemoveNulls(
List.Transform(
List.DateTimes(start, adjNumDays, #duration(Number.Sign(numDays),0,0,0)),
each if _ = start then _
else
if Date.DayOfWeek(_)=Day.Saturday
or Date.DayOfWeek(_)=Day.Sunday
or List.Contains(holidays, Date.From(_))
then null
else _)),
addWorkDays = if numDays = 0 then start else allWorkDates{Number.Abs(numDays)}
in
//List.DateTimes(start, adjNumDays, #duration(Number.Sign(numDays),0,0,0))
//adjNumDays
addWorkDays
Although this is a Power Query forum, if you should want a DAX solution, see direct application of WORKDAY function like in excel
