[SalesForce] Difference between two dates in hours excluding weekends

So I wrote some code to handle this recently. It is completely configurable, and as efficient as can be.

The most important thing is to set the isWorkingDay array with the right flags (index 0 is Monday) and to make sure workingDaysInWeek matches the number of true flags in the array. After that the method will return a value for you.

//array of seven boolean indicating working days, Monday is index 0
private static final List<Boolean> isWorkingDay;
//count of the number of working days in the array
private static final Integer workingDaysInWeek;
static {
    //my real implementation uses the Salesforce BusinessHours Object to populate this array
    isWorkingDay = new List<Boolean> { true, true, true, true, true, false, false };
    //You will have real problems if this number does not match the number of true flags in the array
    workingDaysInWeek = 5;
}
// Monday is January 1st, 1900.
private static final Date monday = Date.newInstance(1900, 1, 1);
private static Integer getDayOfWeek(Date value) {
    return Math.mod(monday.daysBetween(value), 7);
}

public static Integer getWorkingDays(Date startDate, Date endDate) {
    //save some calculations when the number of working days is 0
    if(workingDaysInWeek == 0 || startDate == null || endDate == null) {
        return 0;
    } else {
        Integer difference = startDate.daysBetween(endDate);
        if(difference == 0) {
            //If the 2 dates are the same day check if the day is a working day or not
            return isWorkingDay[getDayOfWeek(startDate)] ? 1 : 0;
        } else if(workingDaysInWeek == 7) {
            //when every day is a working day return the difference
            return difference;
        } else {
            //The guts of the solution
            Integer wholeWeeks = Math.floor(difference / 7).intValue();
            Integer workingDays = wholeWeeks * workingDaysInWeek;
            Integer dayOfWeek = getDayOfWeek(endDate);
            for(Integer remainder = Math.mod(difference, 7); remainder >= 0; remainder--) {
                if(isWorkingDay[dayOfWeek]) {
                    workingDays++;
                }
                dayOfWeek--;
                if(dayOfWeek < 0) {
                    dayOfWeek = 6;
                }
            }
            return workingDays;
        }
    }
}

You are correct - Looking at the SFDC Object reference, Case.closedDate is a DateTime field so line 2 and line 4 will break

Looking at line 2 and line 4 - these are manipulating days, not seconds so I'd rewrite line 2 and line 4 as:

Line 2

( 5 * FLOOR( ( DATEVALUE(ClosedDate) - DATE( 1900, 1, 8) ) / 7) +

Line 4

MOD( DATEVALUE(ClosedDate) - DATE( 1900, 1, 8), 7) +

You should go to the doc and use the feedback form to point this out to SFDC