code: private void verifyTimestamp(X509Certificate cert)
          throws CertPathValidatorException
      {
          String msg = "timestamp";
          if (debug != null)
              debug.println("---checking " + msg + ":" + date.toString() + "...");
  
          try {
              cert.checkValidity(date);
          } catch (CertificateExpiredException e) {
              throw new CertPathValidatorException
                  (msg + " check failed", e, null, -1, BasicReason.EXPIRED);
          } catch (CertificateNotYetValidException e) {
              throw new CertPathValidatorException
                  (msg + " check failed", e, null, -1, BasicReason.NOT_YET_VALID);
          }
  
          if (debug != null)
              debug.println(msg + " verified.");
      }
docs: Internal method to verify the timestamp on a certificate