code: public JWTPayload setNotBeforeTimeSeconds(Long notBeforeTimeSeconds) {
          this.notBeforeTimeSeconds = notBeforeTimeSeconds;
          this.put(PayloadConstants.NOT_BEFORE_TIME_IN_SECS, notBeforeTimeSeconds);
          return this;
      }
docs: Sets the not before claim that identifies the time (in seconds) before which the token MUST
  NOT be accepted for processing or {@code null} for none.
  
  <p>
  Overriding is only supported for the purpose of calling the super implementation and changing
  the return type, but nothing else.
  </p>