It's not exactly the same decade. Otoyomegatari seems to be set in the 1860s, as you can see by the way the women in England are dressing, and Henry's friend said that it was after the Crimean War, which raged on between 1853 and 1856. Emma, on the other hand, is set in the turn of the century, the late 1890s to the start of the Edwardian Era (1901-1914).
I said time period, which is the Victorian Era. Emma started at the Victorian and went to the Edwardian Era for few pages at the end of the manga. While Otoyomegatari will end still being in the Victorian Era. It is the same time period.
I can't say how much I love this Manga. I loved Emma and wanted more. Now I get more. No Emma, but same time period!!!! love it!!!