Question: [Wednesday, 16th Iyar 5781]
Is it permitted for one to listen to music starting from sunset of Lag Bomer, or must wait until nighttime [i..e Tzeis Hakochavim]?
One is to wait and not listen to music until after nightfall.
Explanation: In general, there is a debate in the Poskim regarding if the mourning customs are ceased to be practiced only starting from the morning of Lag Baomer, or from the previous night. Even according to the latter opinion, which is the way we rule in Chabad following the rulings of the Alter Rebbe, one should only begin the celebration and suspension of mourning customs after nightfall, as prior to nightfall it is considered questionably still day and we find regarding many Halachic matters that one should be stringent and treat it like both day and night. Thus, we rule that initially one should not count the Omer until after nightfall. Furthermore, regarding this matter itself we find in the Poskim that on Lag Baomer day one should not play music after sunset, and hence the same would apply to before nightfall on Erev Lag Baomer.
Sources: Nitei Gavriel 48:18; Regarding the dispute if the mourning customs are suspended from the morning or night of Lag Baomer, see: Admur 493:5; Sichas Kodesh 5737 1:703 [printed in Shulchan Menachem 3:34; Shaarey Halacha Uminhag 5:55]; Regarding not playing music after sunset of Lag Baomer, see: Ashel Avraham Butchach Tinyana 493, brought in Piskeiy Teshuvos 493 footnote 1; Maharsham 493 in name of Daas Kedoshim; Minchas Yitzchak 1:111; Shraga Hameir 2:13; Piskeiy Teshuvos 493:11 and footnote 39