The wording in the article seems a bit dubious. 'Ancient' Japan would refer to Bronze and Iron age Japan (the Jomon and Yayoi periods), i.e. roughly the period until the mid-third century AD. The problem here is that the written word only really came to Japan towards the end of the Kofun period (early 6th century), and the first texts from Japan that we know of, the Kojiki and Nihon Shoki, are from the early 8th century. Incidentally, neither of these texts deal with everyday life, but with Japan's creation myths. Although there are indeed mentions of Japan in the 'Ancient' era (there are a number of mentions if the Kingdom of Wa by the Chinese from the 1st century onward), none of these texts go into the detail as to marriage customs in the country. In short, apart from herself being involved in some groundbreaking archeological digs, there is no way she could know anything about the marriage customs of Ancient Japan, as there are simply no written records of that facet of life in that period.

During the Classical period of Japanese history (Yamato and Heian periods, mid 6th century to 1185), women did indeed occupy a greater role on society than they would perhaps in other places in the world. The 8th century has the only female rulers in Japanese history, while the Heian period's greatest writers were women. They were allowed to own property in their own name too. Marriage however, was a different matter entirely. Considering that one's lineage pretty much determined how far one could rise in Kyoto's court, brides were seen as political tools to advance the current or future fortune (depending on whether the family was supplying the bride or bridegroom) of a family. Choices would be entirely in the hands of the family patriarch. These marriages were also rarely, if ever (I cannot find any mentions of it, at least) dissolved. A marriage was a political tool that might occasionally blossom into love. If men wanted to be with their 'true' love, or express their sexuality, they would take on concubines. Affairs were indeed also possible for both sexes in this period, but were frowned upon. Furthermore, considering the highly ritualized nature of the Kyoto court, a woman that wanted to court a man to her bed would have to go through very specific steps (often literary in nature, read Genji Monogatari for a beautiful illustration of that at work), and in the end would have to wait for the man to take the steps that would bring them together. In short, it was much easier for a man to engage in such activity than for a woman.

Either way, neither the ancient nor classical periods had a custom of temporary marriages, at least as far as we can tell from the texts available to us. The term 'temporary marriage' does pop up in reference to women employed as mistresses by westerners from the 17th century onward. The nature of these contracts was to provide financial and legal security for the women (often brothel workers) who would eventually be discarded by the men though. I hesitate to even call these contracts marriages, as the women involved did not live with the men out of a feeling of love (or expression of sexuality). That sentiment could indeed develop over the course of time, but their initial status had nothing to do with affection. The relationship here is more one between employer and employee than one between husband and wife.

For Ancient & Classical Japan i'm relying mostly on the Cambridge History of Japan (volumes 1&2). For temporary marriages with foreigners in the Modern period, try 'Interracial Intimacy in Japan: Western Men and Japanese Women, 1543-1900', by Gary Leupp.

I've never head about this. Is she talking about the aristocratic practice of the men visiting women's quarters at night to see their partners instead of a permanent living arrangement under one household?