If i export cookie from Chrome with "EditThisCookie" extension i see something like this:
{
    "domain": ".youtube.com",
    "expirationDate": 1599457462,
    "hostOnly": false,
    "httpOnly": false,
    "name": "_ga",
    "path": "/",
    "sameSite": "no_restriction",
    "secure": false,
    "session": false,
    "storeId": "0",
    "value": "GA1.2.1666271553.1536385462",
    "id": 1
}
and if i open Cookie databses (file Cookies in app folder) with DBExplorer, i see this:
expires_utc: 13243931062000000
How 13243931062000000 became 1599457462?