SAML2\Assertion::getNotOnOrAfter PHP Method

    public function getNotOnOrAfter()
    {
        return $this->notOnOrAfter;
    }

 public function validate(Assertion $assertion, Result $result)
 {
     $notValidOnOrAfterTimestamp = $assertion->getNotOnOrAfter();
     if ($notValidOnOrAfterTimestamp && $notValidOnOrAfterTimestamp <= Temporal::getTime() - 60) {
         $result->addError('Received an assertion that has expired. Check clock synchronization on IdP and SP.');
     }
 }