[Jakku]

You could use a unix timestamp for this.

When a player logs in:

pawn Код:

SetPVarInt(playerid, "LoginTime", gettime());

When the player leaves:

pawn Код:

public OnPlayerDisconnect(playerid, reason)
{
    new how_long_he_played = (gettime()-GetPVarInt(playerid, "LoginTime"))/60;
    // This will return the amount of time in minutes the player was online. 
    printf("Player was online for %d minutes", how_long_he_played);
}