It says in Ester "בערב היא באה", "in the evening she would arrive", and we learn many important halachos of Purim from that. I wonder, then: are there any laws or customs specific to the night of Purim? Of course, we read Ester by night, but we do that by day also; I'm looking for something unique to the nighttime.
Many communities have a Purim Rov, the purpose of which is to show the community that the Rov's job is actually harder than it seems.
The questions is what part of Purim should he hold court?
He can't hold court by day, since he's drunk and it's forbidden to rule on questions in a drunk stupor (and it won't help, as he'll claim that if he would have been sober, he'd have done a much better job than the real Rov, thank you very much).
So the custom is to hold court by night, when he's still sober.
And there's an Asmachta to this custom - וגם ערב רב עלה אתם וצאן ובקר מקנה כבד מאד
וגם ערב רב עלה - And even at night, a "Rov" should arise
אתם וצאן - You, (the rest of the congregation) should be his sheep,
ובקר מקנה כבד מאד - And in the morning, (after the charade is over), you realize what good of a purchase you made, when hiring your real Rov.
There is in fact a long-standing custom of packing mishloach manos on the night of Purim. (There's a hekesh yod-dalet yod-dalet to binding the lulav.) This doesn't appear in maseches M'gila, but if you look in maseches P'sachim you'll find this:
אור לארבעה עשר בודקין את החמץ לאור הנר
The night of the fourteenth, we check the chametz by the light of a lamp.
Packing mishloach manos! Obviously, they needed a lamp, because that was the only way to see at night in those days. Funny that it should say "check", not "pack"… and funny that it should specify that the mishloach manos is chametz… well, let's read further and see what it says.
כל מקום שאין מכניסין בו חמץ אין צריך בדיקה
You don't need to check containers in which you're not putting chametz.
Okay, so it really is specifically chametz. Weird. Let's see what Rashi has to say about this.
בודקין — שלא יעבור עליו בבל יראה ובבל ימצא
check — so as not to pass it without it being seen and found
Ah, that makes sense. We want to make sure we're packing the mishloach manos properly, so we need a lamp to make sure every food item is found. It is night, after all. So that explains why it says we check. Still not clear why it specifies chametz. Let's continue.
ובמה אמרו ב׳ שורות במרתף
And about what did they say this? Two rows in a winecellar.
Ah, that's the chametz: whiskey aged in wine casks. From here we see that we're supposed to give whiskey as mishloach manos.
Keep in mind that without knowing the accent, the word באה could be in present tense, also. So that would mean "In the evening she is coming".
Esther was coming to the king at night time, and in the morning she returned.
From this, we learn that women come to shul to hear the Megilla at night. It is difficult for them to come at night when there are many small children who have to be in bed early at night before Megillah reading. But, they manage to do it, in some way, even if that means that they attend a special women's "late" reading after the men come home.
Few of them come during the day, because they are busy at home preparing the Mishloach Manot baskets.