I'm having a tough time imagining a scenario where you're in too much of a hurry to spend 30 seconds returning the cart, but not too much of a hurry to buy your merchandise and load it in your vehicle.
Unless you get a phone call just after unloading your shit into your car what sort of emergency allows you to shop but still demands literally no second be spared?
I suppose if it was dire you save those 30s, it's acceptable.
But you would not be immune to being judged by a third party. They wouldn't know the situation is dire unless explaining it, which would take at least a few seconds.