getDailyKey(date) {
        // Truncate value to start of day (e.g. 2021-01-01 12:34:56 -> 2021-01-01 00:00:00)
        // Considering if the user keep changing could affect the calculation, so use UTC time to avoid this problem.
        date = date.utc().startOf("day");
        let dailyKey = date.unix();

        if (!this.dailyUptimeDataList[dailyKey]) {
            this.dailyUptimeDataList.push(dailyKey, {
                up: 0,
                down: 0,
                avgPing: 0,
                minPing: 0,
                maxPing: 0,
            });
        }

        return dailyKey;
    }
Convert timestamp to daily key
@param {dayjs.Dayjs} date The heartbeat date
@returns {number} Timestamp