I found the exchange re Chulin 105a in recent weeks interesting.
My father, from Sighet, formerly Hungary, now Roumania, insists that his family waited four hours. Is there an opinion for four hours? Maybe it is a chumra on keeping three hours?
I do not know the source for that Minhag, although it is unlikely that it is a Chumra on the three-hour Minhag.
However, it could be that the Minhag that you mention is based upon the same reasoning that some give for the Minhag to wait three hours. Perhaps in those areas of Hungary, it was common to eat three meals each day, and thus the time between each meal was four hours.
Alternatively, Rav Ovadyah Yosef in Yabi'a Omer (YD 1:4) cites Sefer Mizmor l'David (#89) who suggests that the practice to wait three hours is based on the view of the Pri Chadash that says that the six-hour waiting period is comprised of six variable hours (Sha'os Zemaniyos), and not 60-minute hours. Accordingly, in the winter when the days are shorter, six variable hours might equal four 60-minute hours. He says that the custom to wait three hours might have evolved from this view, according to which the shortest amount of time to wait (on the shortest day of the year) was three hours, and thus people waited this amount time all year round. As he explains it: "Since in the winter it is permitted, we say 'Lo P'lug Rabanan'. This is because since in the winter three hours suffices, that shows that the taste of meat does not linger in the mouth more than three hours."
The Me'iri writes that the subject of what type of hours (variable or 60-minute) is a Machlokes Rishonim, and he writes that there might be grounds to permit being lenient between *chicken* and milk. (Indeed, I have seen that some people have the Minhag to wait six hours between meat and milk, and four hours between chicken and milk.)
Y. Shaw