Question: I read that one mustn’t eat before counting the omer. Does it make a difference whether I daven maariv early or late?
Answer: The Rema (OC 489:4) writes that when it is time to count the omer one mustn’t eat until they have counted.
There is a machlokes as to when exactly this starts. The Shulchan Aruch Harav (OC 489:17) writes that one mustn’t eat from a half hour before shekia while the Mishna Berura (489:23) writes that one can eat until a half hour before nacht.
Similarly, the Shulchan Aruch (OC 235:2) writes that one shouldn’t sit down to eat half an hour before it’s time to daven maariv, as they may get preoccupied and forget to recite the shema.
Nonetheless, the Aruch Hashulchan (OC 232:16) writes that one who regularly davens maariv in shul is allowed to eat beforehand as they won’t come to forget to recite the shema. Likewise, the Mishna Berura (235:18) writes that one who wants to eat then may do so providing that they ask someone else to remind them. R’ Avraham Yeshaya Pfoifer (Ishei Yisrael 27:19) writes that the same applies to setting an alarm.
Thus, R’ Moshe Feinstein (Igros Moshe OC 4:99) and R’ Binyamin Zilber (Az Nidberu 6:52) write that there is no need to act more stringently with counting the omer than one does with eating before davening maariv. One who regularly davens maariv after nacht may eat supper beforehand without having to be concerned that they will forget to recite kerias shema. Likewise, as nowadays we are accustomed to count the omer after maariv, one may eat before davening and counting (See Rivevos Ephraim 2:129:28).In conclusion, one who regularly davens maariv after nacht can eat beforehand. One who either davens earlier or is davening later than usual should set themselves a reminder on their phone, etc. before sitting down to eat.