Something

    private static int timeZoneHour(int serverHour, IfxUser user) {
        int hour = serverHour+user.getTimeZoneOffset();
        if (hour < 0) hour += 24;
        if (hour > 23) hour -= 24;
        return hour;
    }

    private static int timeZoneOffset(int serverHour, int timeZoneHour) {
        int offset = timeZoneHour-serverHour;
        if (offset < -2) offset += 24;
        return offset;
    }