In short: If you have no stands of a certain size, you might still get a plane of that size in the queue, and there’s no way to remove it, you have to wait 5 minutes and lose the bonus points. (This seems to be happening only with special arrivals.)
This has happened to me several times during the short 2-3 weeks I’ve been playing, and today it bothered me enough to file a bug report. I just started on NGO. Didn’t buy any extra stands and don’t plan to until I have enough to purchase a terminal with X stands. Everything went as expected with my first 10 arrivals. Then I hit Level 2 and got the W10,000 reward plus special arrival. Even though I only had the 3 S stands, the next plane in the queue was the M sized special arrival for the level reward. I decided to be stubborn and not buy an M stand. I had to wait 5 minutes for the card to time out. OK I thought, no biggie, just lost 2 bonus points, back to 0, just lost 5 minutes, not too bad. Then I hit the speed up button to get the next card and move on towards level 3 and the BAE146 reward. But all that got me was an X sized Cargolux arrival. Ugh another 5 minute wait, no losing bonus points because I’m already at 0… And next after that, the L-sized Concorde arrival…!!! As I write this, those 5 minutes are expring… Finally, an S-sized golden! And the next one is a regular S arrival, it looks like things are back to normal… for now at least… But having to wait for 15 minutes watching the planes expire is simply no fun 
