Based on the 2019 rewatchalongs (links). The duration in days is an estimation, and generally doesn't include any of the non-case matters in the episodes, which might've taken up a day or so.

Months from start	Case	Episodes	Lasts (days)
0	Sundial/intro	1, 2	4?
	Rapid aging	3	2
0.5	Face stealer	3, 4	2
	Bathroom kidnappings	5	3+
	Mirror girl	5, 6	4
	Webnovel murder	7	2 (3?)
1	Ding Dun	8	2?
	Hanga arc	9-11	3?
	Doom sounds/identity reveal	11-14	4?
	Cong Bo	14, 15	2
3	Soil/Dixing trip	15-17	3-4
4
5
6	Fight Club/Zhu Jiu endgame	17-20	3
6.5	Miracle doctor	21, 22	5?
	Dixing's new king	22, 23	2?
	Video game	23, 24	2
	Personality change	24, 25	4
	Da Ji/MOMB identity	26	4?
	Merit Brush endgame	27-29	5-ish
	Shen Wei pillar BDSM	30	-
	Zhu Hong dream	31	2
	Chu Shuzhi dream	32,33	3
	Shen Wei pillar rescue	33	(6? days of BDSM)
	SID disbanding	34	1
	Time travel	34-35	2 (in the present)
9.5	Mi Lu/Yashou branch (wick search)	37, 38	1?
	Endgame showdown	38-40	1? 2?
21.5	Epilogue	40	1?

Other notes:

• I'm relatively sure that there was a timeskip between the doom sounds/identity reveal case and the visit to Dixing, beyond the canon minimum of 2-3 days, since Zhu Jiu needs time to heal up a bit and the doom sounds seems to flow straight from the Hanga stuff, which flows straight from the 1-month marker. So the identity reveal would be under 2 months in?


• The time travel segment in the past was probably about a month, since that's the amount of time it takes to make baijiu, but they were excised from the present for 2 days.


• The endgame showdown with Ye Zun is probably on the same day as the Yashou branch thing, and the entire stretch from the Merit Brush endgame to the end is one segment without significant timeskips.