system/I18n/Time.php
public function difference($testTime, string $timezone = null)
	{
		$testTime = $this->getUTCObject($testTime, $timezone);
		$ourTime  = $this->getUTCObject($this);

		return new TimeDifference($ourTime, $testTime);
	}
public function difference($testTime, string $timezone = null)
	{
		$testTime = $this->getUTCObject($testTime, $timezone);
		$ourTime  = $this->getUTCObject($this);

		return new TimeDifference($ourTime, $testTime);
	}
@param $testTime
@param string|null $timezone

@return \CodeIgniter\I18n\TimeDifference
@throws \Exception