The Fullness of Time

The original 1962 magazine version was abridged for the 1962 Times Without Number collection. The latter version was in turn slightly revised and expanded for the 1969 edition of Times Without Number, which was used in all subsequent reprints, prior to the 2020 publication of The Society of Time collection, which uses the original magazine version. The publisher's description for the latter collection indicates that, at least in that original form, this story is novella length.