When Erev Pesach was on Shabbat, nearly every shul rav I have encountered has advised this procedure on Shabbat morning:
Daven very early so that Shabbat davening will end before the last time one is allowed to eat chametz.
Go home, wash and eat a meal with challah. Then bentch, and wash again and eat another meal with challah. This way, you will have eaten your 3 Shabbat meals all with challah.
I have read that one may fulfill Se'udah Shlishit eating fruit and one may also eat matza ashirah on Erev Pesach. For some reason, the rabbis insist that all 3 meals should have challah / chametz.
Considering this answer that explains that Seudah Shlishit must be eaten in the afternoon, which, in this case, would be after the time one would be allowed to eat chametz, how do these rabbis suggestions accomplish having the 3rd meal immediately after the second, as they suggest?