pTimes[MAX_PLAYERS]; // Top of the script
forward SecondTimer(); // Top of the script

SetTimer("SecondTimer", 1000, 1); // Below OnGameModeInit()

public SecondTimer()
{
    for(new i = 0; i < MAX_PLAYERS; i++)
    {
        if(IsPlayerConnected(i) && pInfo[playerid][pLogged] == true) // I'm not sure, is your variable pLogged or not.
        {
            pTimes[i]++;
        }
    }
    return 1;
}

public OnPlayerDisconnect(playerid, reason)
{
    new string[128];
    // Example 'users' is your tablename, you can change it
    format(string, sizeof(string), "UPDATE users SET times = '%d' WHERE username = '%s'", pTimes[playerid], PlayerName(playerid));
    mysql_query(string);
    return 1;
}

pTimes[playerid] / 24; // 24 = minutes, example the player has played 86 Minutes, 86 / 24 = 3,5 the server converts it to integer automatically, so it's 3 Game Days

pTimes[playerid] / 1140; // A day has 1140 minutes, 60 * 24 = 1140:

new pJoined[MAX_PLAYERS];

public OnPlayerConnect(playerid)
{
    new pJoined[playerid] = gettime();
    return 1;
}

public OnPlayerDisconnect(playerid, reason)
{
    new value = gettime() - pJoined[playerid];
    printf("The player has played %d minutes.", value);
    return 1;
}