What is the latest time before Tseis Hakoichovim that one can wash for Shalosh Seudos? What if one keeps Rabeinu Tam? Till when can one eat if one doesn’t wash (only Mesoinois)? We follow Minhag Ashkenas and live in Vienna, Austria. Thank you!
Since you keep Rabbeinu Tam, you can start eating as long as it is still Bein Hashmashos (1). In Israel this is 13 and a half minutes after shekia. Please ask a local Rav when that time is in Vienna.
There is no difference between bread and mezonos, since you are eating the mezonos for Shalos Seudas.
All the best
(1) Mishna Berura 299:1 and Shaar HaTzion 299:3, Ketzos Hashulchan siman 94 Baadai Hashulchan 6.