Displaying TimeSpan as largest interval (with units)

Question

The following method is used in a call center application to display an approximation of remaining time. The call center telephone operator would inform the caller that they could perform their desired action (like, for example, place another order) after N time has elapsed. You'll note some arbitrary rules revolving around the interpretation of time embedded within the method, e.g., an interval greater than 50 minutes is considered to be "1 hour"; these business rules need to remain as is.

With that in mind, are there any suggestions on how this routine might be enhanced and/or improved (i.e., made more efficient)?

_{N.B. Obviously, the millisecond case (the "else") is not practical, but only included now for the sake of completeness. It may, in the end, be converted to something like 'less than 3 seconds' equals "now". For the sake of this question, however, let's go with the routine as written.}

public static string LargestIntervalWithUnits(TimeSpan interval)
{
    if (interval < TimeSpan.Zero)
    {
        throw new ArgumentOutOfRangeException("interval");
    }

    if (interval == TimeSpan.Zero)
    {
        return "now";
    }

    int timeValue;
    string timeUnits;

    if (interval.TotalHours > 22.0)
    {
        timeValue = (int)Math.Ceiling(interval.TotalDays);
        timeUnits = " day";
    }
    else if (interval.TotalMinutes > 50.0)
    {
        timeValue = (int)Math.Ceiling(interval.TotalHours);
        timeUnits = " hour";
    }
    else if (interval.TotalSeconds > 40.0)
    {
        timeValue = (int)Math.Ceiling(interval.TotalMinutes);
        timeUnits = " minute";
    }
    else if (interval.TotalMilliseconds > 500.0)
    {
        timeValue = (int)Math.Ceiling(interval.TotalSeconds);
        timeUnits = " second";
    }
    else
    {
        timeValue = (int)Math.Ceiling(interval.TotalMilliseconds);
        timeUnits = " millisecond";
    }

    return string.Format("{0:#,##0}{1}{2}",
                         timeValue,
                         timeUnits,
                         (timeValue == 1 ? string.Empty : "s"));
}

_{Edit: Subsequent refactored code block, that was added after answers were posted, has been removed per users' suggestions. (This note has been added to clarify comments posted by users.)}

_{Edit 2: The code listed above has been refactored and reposted for further review: Displaying TimeSpan as largest interval (with units) [Part II]}

Answer 1

The numbers 22.0, 50.0, 40.0, and 500.0 are "magic numbers" (non-obvious hard-coded numbers with no given meaning).

Since they're not commonly used with time, thus are not obvious, you should make the reader aware of their meaning. This will also improve readability.

Two options for doing this include:

1. making them into constants with appropriate names

   private static readonly double someConstant = 22.0;
   // remaining constants
   

2. providing comments or full documentation on their meaning

Answer 2

Depending on how you are calling this piece of code, this if statement will almost never be evaluated as true.

if (interval == TimeSpan.Zero)
{
    return "now";
}

I don't think it is worth the time to type this out, it should be grouped into the else statement

else {
    timeValue = (int)Math.Ceiling(interval.TotalMilliseconds);
    timeUnits = " millisecond";
}

or rather

else {
    return "now";
}

Answer 3

Minor issue, but timeUnit should not hold " " + timeUnit. The space is a formatting concern, and thus should be placed in the format string used by string.Format.

Also, the exception thrown here could be a little more descriptive otherwise the caller may be confused what was wrong with the interval:

if (interval < TimeSpan.Zero)
{
    throw new ArgumentOutOfRangeException("interval", "reason why it's out of range");
}