On my previous flight from Amsterdam to Tokyo two years ago, about an hour before the seat belt lights came on for landing, we were given our customs declarations form (I'm a UK citizen). I was spending less than 90 days there so I did not have to apply for a visa.
My upcoming flight will have me arrive in Tokyo early in the morning, so I was hoping to sleep for most of the flight with as few interruptions as possible (which I can appreciate on an 11-hour flight is optimistic!). As such, I was planning on asking the cabin crew if I could be given my immigration and customs paperwork at the earliest opportunity during the flight so I can take my time filling it out and not worry about it later. On a personal note, it also removes one less item of stress from the journey.
Are there any laws or common airline-enforced practices that would prevent me from being given my customs paperwork so early in a flight (especially if the flight is to Japan)?