Q. Dear Rov. On the first night of Shavuot the meal usually finishes very late. Someone went to sleep and woke up early to daven with the Netz (sunrise) Minyan, if on the night meal one ate meat, can he drink a coffee with milk before davening, even if no six hours have passed since the end of that meal?
A. Some Poskim are lenient and in general don't require a wait of six hours exactly. They lenient even when most or even part of the sixth hour has passed (minhag of Lakewood Yeshiva).
Others are lenient after sleeping a night sleep, and maintain that then less than six hours suffice.
Horav Y. D. Harpenas (Mekadesh Yisroel - Shavuos 85) quotes the lenient Poskim and also a story from Zichron Moshe who relates that the Chassam Soffer wanted to be lenient and not require six full hours when sleeping, since then the digestion accelerates. However, he retracted when he saw as a sign from Heaven and the coffee with milk cup spilled.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a.