I believe this is more a question more suited a subreddit related to the economy, rather than history, mainly because the 'struggle for shorter working day' never stopped, but decelerated instead. In general, the decrease in the upper limit of work time employers could have demanded from the employees was mitigated by the obvious fact that work, although limiting the free time, was also a main mean to provide income. And because of that, the changes in the work time sooner or later were destined to meet a sui generis equilibrium, where an adequate pay was provided in exchange for adequate effort, both from the employee's and employer's point of view. In the 1950's the quote 'eight hours labor, eight hours recreation, eight hours rest' attributed to Robert Owen, 19th century entrepreneur and a labour activist became the norm in the Western world and Warsaw Pact countries. This is influenced by plethora of factors with population, education, development rate, GDP both total and per capita, wealth distribution, legal system, taxation and trade relations with foreign countries playing quite an important role. I do not even try to address the model, as I am not an economist, but suffice to say, it is a complex one.

If you take a look at the average working time in particular countries, you will notice that it is usually inversely proportional to the relative wealth (expressed as e.g. GDP per capita and Gini coefficient). For example, people work the longest time in well developed, large but not necessarily wealthy countries, such as Mexico, China, Russia or Poland, while the wealthy countries usually take much lower positions on such ranking. According to the 2016 data collected by OECD and IMF, among the countries with the highest average number of hours worked monthly is: China (199 h), India (192 h), Mexico (188 h), Russia (162 h) or Poland (160 h), while the richest European countries enjoy far less working hours, e.g. Luxembourg (119 h), Netherlands (118 h), Norway (117 h), Denmark (116 h) or Germany (113 h). Comparing this with the GDP per capita as Purchase Power Parity gives us the following numbers for the first group: China - $18100, India - $7874, Mexico - $20602, Russia - $29200 and Poland - $31939, while for the second group it is: Luxembourg - $106700, Netherlands - $56400, Norway - $74350, Denmark - $52100 and Germany - $52500.

Now, in 'wealthy countries' the aforementioned 'struggle' apparently not only has not stopped but is very much alive and brings results. With good employment rates provided by a thriving economy, high automatization allowed by adequately high technological development and high wages with relatively good social security systems, courtesy of high revenues, employees tend to work less than 8 hours, as evidenced by the data above. Furthermore, France officially adopted a 35-hour work week in 1995, decreasing the length of an average working day from 8 to 7 hours. In Netherlands, an average work week length fell to 30 hours in the middle of the first decade of the 20th century, making it the first highly developed country to de facto employ 6-hour work day. Such attempts are not too common, mainly because in most cases wages are too low to allow the contemporary lifestyles after being e.g. cut in half if we're speaking about 4-hour work day.