From myzemanim.com for where I live, for this Shabbos, erev Shovuos, the “sho’o zemanis” (Proportional Hour) Gra & Baal Tanya is 1hr:22mins. Nightfall - 3 Stars is around 10:30 pm. Shkia is around 9:20 pm.
How do I calculate the latest time to start Sholosh seudas “sho’o asiris”?
Are there any leniencies bearing in mind the length of the sho’o zemanis?