When EREV PESACH is SHABBOS, can one eat EGG MATZA for Third meal? Is there a time restraint?
The Ashkenazi minhag according to many is not to eat egg matzoh on erev Pesach, at all. Some poskim say that it is permitted until the when we may eat chometz on erev Pesach. Even the Sefardim who do eat egg matzoh on erev Pesach will only do so until the beginning of the tenth hour of the day.
Therefore we do not eat egg matzoh for shalosh seudos, unless you will eat it very early, but then you can eat regular rolls. What some people do, is to eat Pesach cake or knaidlach for the third meal, however since we are to eat the matzoh with an appetite we don’t eat mezonos past the beginning of the tenth hour of the day. Therefore, if one is eating mezonos for shalosh seudos on Shabbos erev Pesach it has to be before that time.
Rema 462-4, 472-1, Chelkas Yackov Gr”a 444-7, Shar hatzion 444-1, Yesodei Yeshurin 6:pages 63-67; Ashrei Ha’ish, O.C. 3:page 370:11, Gra”z 444-3, V’yashav Moshe 2-98, Igros Moshe O:CH 1-155.