Shulchan Aruch Orach Chaim 620 says that one should daven Musaf before the seventh hour of the day on Yom Kippur even if it means leaving out Piyutim and Selichos of Shachris. Mishna Berura says to even leave out Avinu Malkeinu if necessary. The Tur there implies one should even ensure to start by 6.5 hours into the day.
Some Chasidim do not start Musaf till later than that and on Simchas Torah even many non Chasidim do not Daven Musaf prior to the seventh hour. Is there any reason for not keeping this recommendation on the Shulcan Aruch? Is Simchas Torah in the Diaspora more lenient since it is Yom Tov Sheni?
Aruch Hashulchan 620:2 says that there are those that dispute that one would have to pray Mincha before Musaf once the time for Mincha arrives. It is especially reasonable that on Yom Kippur that this would be disputed because many say the reason for having to reverse the order has to do with the fact that one may not eat once the time of Mincha arrived until praying Mincha, which is not relevant on Yom Kippur since all are fasting anyway.