Compare two ways to do the same validation. In both cases, the values for `StartTime` and `EndTime` are strings in the view models, hence the reason they need to be parsed at the beginning of the method.

gistfile1.cs

// First version
// 1. Multiple return statements (> cyclomatic complexity)
// 2. 'Happy' path comes first
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
  var startTime = TimeSpan.Parse(StartTime);
  var endTime = TimeSpan.Parse(EndTime);

  if (startTime < endTime)
    return new ValidationResult[] { };
  
  return new [] { new ValidationResult("Start Time must be before End Time", new [] { "StartTime", "EndTime" }) };                
}


// Alternate version
// 1. Less cyclomatic complexity
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
  var validationResults = new List<ValidationResult>();

  var startTime = TimeSpan.Parse(StartTime);
  var endTime = TimeSpan.Parse(EndTime);

  if (endTime >= startTime)
    validationResults.Add(new ValidationResult("Start Time must be before End Time", new [] { "StartTime", "EndTime" }));

  return validationResults;
}