code: public Subclass withIAMTokenRefresh(double offset) {
          this.iamTokenRefreshOffset = offset;
  
          if ((offset > 0) && 
          		(this.credentials.getCredentials() instanceof IBMOAuthCredentials) &&
          		((IBMOAuthCredentials)this.credentials.getCredentials()).getTokenManager() instanceof DefaultTokenManager){
          			((DefaultTokenManager)((IBMOAuthCredentials)this.credentials.getCredentials()).getTokenManager()).setIamRefreshOffset(iamTokenRefreshOffset);
          }
          return getSubclass();
      }
docs: Sets the time offset used for IAM token refresh by the DefaultTokenManager.
  This should only be over written for a dev or staging environment
  
  @param offset, percentage of token life before expiration that token should be refreshed.
  @return This object for method chaining.