Sodom also at Passover: Rev 11:8 (Sodom and Egypt, where also our Lord was crucified: witness of Sodom at Passover).
Shelamim! cf. bPesahim 60a-b: transformation of the Passover sacrifice into Shelamim.
Levit was probably going to Bethel (17:19; cf. Edenburg 2018, p. 291).
Bethlehem: 5 days of preparation, since Nisan 10. it seems that the nychtemeron starts at the down.
Jerusalem (Bethel) vs Gibeah (also a shrine, cf. Edenburg). Mitzpah is secular only (cf. Edenburg).
2. Therefore: 3 battles falling on Pentecost (even if Pinehas is a later addition). Why Pentecost (and not Passover of the next year): 1. the main motive here is the renovation of the Covenant; 2. four-month interval before the next feast(s) which is (are) twofold (10 and 15.VII).
3rd battle falled on Pentecost. Probably, one day of fasting (Sabbath).
Chronology: Thu: 1st battle, Fri: 2nd battle, Saturday (the most important sacrifice), 3rd battle, Sunday.
3.5-day of fasting with the victory after the last (fourth) night?
Smoke on Gibeah: a parallel with Sodom but on the Pentecost?
3. Final episodes four months later (thus, in Tishri): 10 (reconciliation with the rest of Benjamin and judgement on Jabesh Gilead) and 15 Tishri (Shiloh? perhaps still Bethel or a competence with Shiloh?): Sukkot (agricultural rituals outside the walls of the city, vines).
Cf. independent source: Flavius Josephus mentions some fast (cf. 10.VII).
4. Beginning of the whole story and the meaning of Jud 19:2 (the modern consensus is false, cf. Edenburg, but cf. Lagrange1903: 296 following Moore, which I take mutatis mutandis: וַתִּזְנֶה עָלָיו as a Rabbinic correction of ותנאף, while ὠργίσθη αὐτῷ going back to the misspelling ותאנף). The topic of WATCHERS!
Calendar: 10.I the first day in Bethlehem, the one-day travel on 9.I = the first day after the four months of separation (19:2-3). Thus, the four-month period ended on 8.I and, therefore, started on 8.IX (the day of the separation itself).
8.IX: cf. cult of Michael, esp. in Coptic, and 8.IX in the Liturgy of the 49th Sabbath: Watchers and Michael.
cf. 8.IX in the Liturgy of the 49th Sabbath, where it is the 7th Sabbath after the Sabbath of Sukkot. Anyway, the story in Jug 19-21 covers the entire liturgical year, from Sukkot to Sukkot. cf. LAB 45:6 "adversary" (Satan).
5. Wathers' motives (1 En 6-9, the part of 1En that is a quotation from an earlier source, could be earlier than 3rd cent.; cf. Yoshiko Reed 2006; thus, roughly contemporaneous to Judges (late 6th or 5th cent.)).
1 En 6:3-4 oath to take wives: cf. the oath of the Israel not to give wives to Benjamin.
1 En 7:15 anthropophagy: cf. Levit's concubine as Shelamim.
1 En 9:1, 9 bloodshedding: cf. battles.
Judges: Benjamenites took their wives in the manner symmetrical to (correcting?) the act of the Watchers.
6. Conclusion: Judges 19-21 was a self-standing work related to the story of the Fall of the Watchers (perhaps in its pre-Enochic form). The sin of Levite's concubine/wife was adultery with Watchers or something of this kind, equally inacceptable for the editor of the Judges.