Slightly premature, but...
Since the initial post on 1/20/2017, this thread has grown and grown. Out of curiosity I looked at the dates for various "milestone" post numbers.
5000th post 5/25/2017 (125 days after 1st)
10000th post 8/4/2017 (71 days after 5K)
15Kth post 12/15/2017 (133 days after 10K)
20Kth post 2/16/2018 (63 days after 15K)
25Kth post 4/20/2018 (63 days after 20K)
30Kth post 6/16/2018 (57 days after 25K)
35Kth post 8/17/2018 (62 days after 30K)
40Kth post 10/14/2018 (58 days after 35K)
45Kth post 1/3/2019 (81 days after 40K)
50Kth post 2/21/2019 (49 days after 45K)
55Kth post 3/30/2019 (37 days after 50K)
60Kth post 5/22/2019 (48 days after 55K)
65Kth post 8/5/2019 (75 days after 60K)
70Kth post 10/3/2019 (59 days after 65K)
75Kth post 11/6/2019 (34 days after 70K)
80Kth post 1/6/2020 (61 days after 75K)
85Kth post 2/21/2020 (46 days after 80K)
90Kth post 3/29/2020 (37 days after 85K)
95Kth post 6/3/2020 (66 days after 90K)
100Kth post 8/7/2020 (65 days after 95K)
105Kth post 10/2/2020 (56 days after 100K)
110Kth post 10/31/2020 (29 days after 105K – a record!)
NOTE: Due to post deletions, some data may be incorrect now.