Q. Can you help the luz bone nutrition if you also eat at the end of shaleshudes, after the zeman but before bentching a kezais of chala and declare it should be for melave malka? Can you combine this with just eating mezonos later on after havdala, as in the prior question?
A. Mishna Berura (300: 2) writes that on should eat melave malka as soon as possible after the end of Shabbos. Eliahu Rabbah (ibid. 1) indeed mentions that one could eat a kezais of bread at the end of the third meal, with the intention to comply with the melave malka seuda. However, other Poskim disagree (Piskei Teshuvos, ibid. n. 48).
Horav Shlomo Miller’s Shlit’a opinion is that one cannot combine the above. When in some need, one should just eat later mezonos.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a