The chiyuv of simcha on yom tov through drinking a revi’is wine is just one time a day or twice a day, by day and by night?
The obligation of drinking wine applies to each meal of Yom Tov (see Mishnah Berurah 529:11).
Although some write that today, the obligation will not apply (see Mo’adim Uzemanim 7:111), see Devar Moshe Vol. 1, no. 11 who writes that the obligation does apply even today.
Many write that the obligation is to drink a full revi’is, but this is not agreed on by all poskim (see Mikra’ei Kodesh Pesach 35; Or Le-Zion 3:15:4; Shut Birkas Yehudah 36; Kovetz Or Yisrael 5 p. 65).