Detta är 1973-novellen " Var var du senast Pluterday? " av Paul van Herck
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The theme in the book is Pluterday, an extra day in the week which can be withdrawn if one saves enough time (e.g. by taking a plane instead of a train). Only the rich can save enough time and thus Pluterday is in practice reserved for the "happy few", resulting in a class society. The existence of Pluterdays is kept secret to non-privileged people.