Epicor's System sets an Automatic Due Date from your Company Config table... But if you say +3 days... it doesnt care if its a weekend or a holiday... Lets check the Production Calendar and assign a proper DueDate.

Quote.GetNewQuoteHed.POST.p

/* Specify the DueDate */
def var newDate as Date init Today no-undo.
def var totalDays as Integer init 0 no-undo.
def var validDateFound AS LOGICAL init false no-undo.
def var calName as Character init "MAIN" no-undo.

for each ttQuoteHed where ttQuoteHed.RowMod = "A".
	if (ttQuoteHed.Quoted eq false) THEN DO:

			/* Initialize */
			assign newDate = ttQuoteHed.DueDate.

			for first ProdCal fields (BeginWeekday WorkWeek) where ProdCal.Company = CUR-COMP and ProdCal.CalendarID = calName no-lock.
						/* Search for a Valid WorkDay */
						do while validDateFound = false:

							/*{lib\PublishInfoMsg.i &InfoMsg=string(newDate)}.*/

							/* Make sure the WeekDay is not a Saturday or a Sunday */
							if weekday(newDate) <> 1 and weekday(newDate) <> 7 then do:

								/* If its not the Weekend make sure it is a WorkingDay */
								find first ProdCalDay no-lock where ProdCalDay.CalendarID = calName and ProdCalDay.ModifiedDay = newDate and ProdCalDay.WorkingDay = false no-error.

								/* If its not a WorkingDay try going a date back */
								if not available(ProdCalDay) then do:
									if ProdCal.WorkWeek[ weekday(newDate) ] = true then do:
										assign validDateFound = true.
									end.
								end.
							end. /* if */

							/* We dont have a valid date lets try next day */
							if (validDateFound eq false) THEN DO:
								assign newDate = newDate + 1.
							END.
						end. /* while */
			end.


		/* Assign New Due Date */
		assign ttQuoteHed.Date02 = newDate.
		assign ttQuoteHed.DueDate = newDate.
	END.
end.