function getOriginalVisitorCookieTimeout() {
                var now = new Date(),
                    nowTs = Math.round(now.getTime() / 1000),
                    visitorInfo = self.getVisitorInfo();
                var createTs = parseInt(visitorInfo[2]);
                var cookieTimeout = 33696000; // 13 mois en secondes
                var originalTimeout = createTs + cookieTimeout - nowTs;
                return originalTimeout;
            }
https://support.google.com/analytics/answer/7476333?hl=en
https://developers.google.com/analytics/devguides/collection/gtagjs/cross-domain