[TheArcher]

OnPlayerUpdate doesn't call the commands per second but per 100ms if i'm not wrong.

Edit: I saw your script after my answer.

pawn Код:

if(g_switch[playerid])
    {
        SendClientMessage(playerid, -1, "Update/sec..");
    }

1° I think this make no sense. In that case will update the message a lot every second when g_switch is called, but it must be called with true or false at the end.
2° return true / return false, is not equal to return 1 / return 0 .