Depending on the flight load, you might only get one bus anyway. Additionally, my recollection is that both buses leave at the same time once deboarding is fully complete (but I may be confusing this with the experience on another airport ... too many remote stands lately). On a short connection, I suggest you forget the lounge, even on intra-Schengen flights where there is no security and border crossing, your priority is to be at your gate before it closes, KL will not wait for you. From personal experience, unless there are disruptive operational circumstances, a 40-min connection in AMS, even with remote stand arrival, is doable.