Commentary for Berakhot 5:2

because we cant say that the time of the day becoming holy and the time in witch the priests come in to eat the tithings is the same because if this were the case then the opinion of r Eliezer would be the same opinion of r yehoshua

In the Mishnah, R. Eliezer's time-standard is when the priests enter to eat the Terumah (i.e. the appearance of the stars) ; in the Baraita, it is when the Sabbath is hallowed (i.e. sunset).