[tommie113]

Put your timer in a handle and make it equal to INVALID_HANDLE.
Check at players spawn to only create the timer if that handle equals to invalid handle.
This should prevent the timer from being created twice.
Don't forget to CloseHandle on your timer handle and set it's value back to invalid_handle or you get problems next spawn.

[Blowst]

PHP Code:

Handle g_hSpawnTimer[MAXPLAYERS+1];

public Event_OnPlayerSpawn(Handle:event, const String:name[], bool:dontBroadcast)
{
    
    new client = GetClientOfUserId(GetEventInt(event, "userid"));
    ClearHandle(g_hSpawnTimer);
    g_hSpawnTimer = CreateTimer(1.0, Stuff, client);
}


public Action Stuff(Handle timer, any client) 
{
    if (client > 0 && IsPlayerAlive(client) && IsClientConnected(client))
    {
        if (IsPlayerGenericAdmin(client))
        {
            SetEntProp(client, Prop_Send, "m_ArmorValue", 100, 1); //armor
            SetEntProp(client, Prop_Send, "m_bHasHelmet", 1); //helmet
            GivePlayerItem(client, "weapon_hegrenade"); //grenade
            GivePlayerItem(client, "weapon_flashbang"); //flash
            CPrintToChatAll("{red}%N {orange} jest graczem {purple}Premium{orange}!", client);

        }else
        {
            SetEntProp(client, Prop_Send, "m_ArmorValue", 100, 1); //armor
            SetEntProp(client, Prop_Send, "m_bHasHelmet", 0); //helmet
        }
    }
}

stock void ClearHandle(Handle& hndl)
{
    if(hndl != null)
    {
        delete hndl;
        hndl = null;
    }
}