Thus, according to all views, one must eat a ke-zayit (olive’s bulk) of matza by itself. The dispute between Hillel and the Sages only affects what is done thereafter:
According to the Sages, after eating the matza one must eat a ke-zayit of maror by itself, and the maror is not to be eaten with the matza. It is true that we saw Rishonim who are of the opinion that according to the Sages one may eat the maror along with the matza, but even according to this view that would only be true when the Temple stood, when a person could fulfill the two commandments together. Nowadays, when one must eat the ke-zayit of matza by itself, one may not eat the matza along with the maror. This is because once one has eaten matza, eating more matza is optional but not required, and one cannot mix the eating of maror, which is required by rabbinic decree, with the eating of matza, which is now an optional act (just as one does not mix an eating requirement by Torah law with one which is only by rabbinic decree). Therefore, had we ruled according to the Sages, we would say that the matza and the maror must be eaten separately.
On the other hand, according to Hillel, as ideally the commandment is to eat the matza together with the maror, thus, even though we must eat the matza by itself nowadays, we still have the obligation to make a remembrance of the Temple practice and to eat the two together, thereby fulfilling the commandment to eat maror. According to Hillel, we do not say that after one has eaten the matza, the later eating of matza will be optional and will nullify the taste of the maror in the “sandwich,” because eating the maror is by rabbinic decree as is the eating of matza along with the maror, since eating the two together serves as a remembrance of the Temple practice. Thus we have here two rabbinic decrees, where one does not nullify the other. Therefore, if we had ruled in accordance with Hillel, we should have said that one is to eat a ke-zayit of matza and afterwards to eat a ke-zayit of maror along with a ke-zayit of matza (all of this is according to Tosafot ibid., s.v. ella; Rosh, 27; Ran, 25a in the Rif’s pagination; and others).
Now, given that the Gemara did not reach any decision, we follow both views:
a) We start by eating a ke-zayit of matza (which is required by both the Sages and Hillel, because eating matza is required by Torah law, and one cannot mix it with maror, which is only is rabbinic ordinance).
b) Afterwards, we eat a ke-zayit of maror (in accordance with the view of the Sages, that one does not mix the eating of maror, which is a rabbinic ordinance, with matza, which at that point is only optional).
c) Finally, we eat matza together with maror (according to Hillel, who ruled that at the outset that is the way to fulfill the eating of maror, as was done in the Temple).
As mentioned, according to Hillel it would be appropriate in our times to eat a ke-zayit of matza, and immediately afterwards eat the korekh. However, out of concern for the view of the Sages, we eat the ke-zayit of maror separately before the korekh. In light of our custom, one can ask whether, according to Hillel, one fulfills the commandment of maror when eating the maror or when eating the korekh.