[Jay_]

Код:

static n_PlayerOnline[MAX_PLAYERS];

public OnPlayerConnect(playerid)
{
  n_PlayerOnline[playerid] = GetTickCount();
}

stock GetOnlineSeconds(playerid)
{
  return GetTickCount() - n_PlayerOnline[playerid] * 1000;
}

That will check seconds. I've made a function in the Useful Functions topic for converting seconds to hours / minutes.