Most often in August, 31 days.
Highest follower count seen that year: 4,795.
July
Jul 28 14:00–17:00, 20:00–21:00 UTC Jul 29 15:00–16:00, 20:00–22:00 UTC Jul 30 19:00–21:00 UTC Jul 31 20:00–22:00 UTC
August
Aug 1 19:00–22:00 UTC Aug 2 19:00–21:00 UTC Aug 3 21:00–22:00 UTC Aug 4 16:00–17:00, 20:00–22:00 UTC Aug 5 19:00–21:00 UTC Aug 6 20:00–22:00 UTC Aug 7 20:00–22:00 UTC Aug 8 20:00–23:00 UTC Aug 9 20:00–23:00 UTC Aug 10 14:00–15:00, 18:00–20:00 UTC Aug 11 20:00–22:00 UTC Aug 12 14:00–15:00, 22:00–24:00 UTC Aug 13 15:00–17:00, 20:00–22:00 UTC Aug 14 21:00–22:00 UTC Aug 15 14:00–15:00, 19:00–22:00 UTC Aug 16 14:00–16:00, 19:00–21:00 UTC Aug 17 14:00–15:00, 19:00–21:00 UTC Aug 18 05:00–07:00, 19:00–20:00 UTC Aug 19 05:00–06:00, 16:00–21:00 UTC Aug 20 05:00–06:00, 20:00–22:00 UTC Aug 21 05:00–06:00, 19:00–21:00 UTC Aug 22 05:00–07:00, 20:00–21:00 UTC Aug 23 05:00–06:00, 20:00–21:00 UTC Aug 24 05:00–06:00, 20:00–22:00 UTC Aug 25 05:00–06:00, 20:00–22:00 UTC Aug 26 20:00–22:00 UTC Aug 27 05:00–06:00, 20:00–22:00 UTC Aug 28 05:00–06:00, 20:00–22:00 UTC Aug 29 05:00–06:00, 21:00–22:00 UTC Aug 30 06:00–07:00, 20:00–21:00 UTC Aug 31 05:00–06:00 UTC
September
Sep 1 19:00–20:00 UTC Sep 2 05:00–06:00, 19:00–20:00 UTC Sep 3 05:00–06:00, 20:00–22:00 UTC Sep 4 05:00–06:00, 20:00–22:00 UTC Sep 5 21:00–22:00 UTC Sep 6 05:00–06:00 UTC Sep 7 06:00–07:00, 19:00–22:00 UTC Sep 8 05:00–06:00, 20:00–22:00 UTC Sep 9 20:00–22:00 UTC Sep 10 05:00–06:00, 19:00–21:00 UTC Sep 11 20:00–22:00 UTC Sep 12 20:00–22:00 UTC Sep 13 05:00–06:00, 20:00–22:00 UTC Sep 14 05:00–06:00, 19:00–20:00 UTC Sep 15 05:00–06:00, 20:00–22:00 UTC Sep 16 05:00–06:00, 20:00–22:00 UTC Sep 17 05:00–06:00, 20:00–22:00 UTC Sep 18 05:00–06:00, 20:00–22:00 UTC Sep 19 20:00–21:00 UTC Sep 20 05:00–06:00, 20:00–22:00 UTC Sep 21 06:00–07:00, 20:00–22:00 UTC Sep 22 05:00–06:00 UTC Sep 23 20:00–21:00 UTC Sep 24 05:00–06:00, 20:00–23:00 UTC Sep 25 20:00–22:00 UTC Sep 26 21:00–22:00 UTC Sep 27 05:00–06:00, 20:00–21:00 UTC Sep 28 20:00–22:00 UTC Sep 29 05:00–06:00, 20:00–22:00 UTC Sep 30 05:00–06:00, 20:00–21:00 UTC
October
Oct 1 19:00–21:00 UTC Oct 2 05:00–06:00, 20:00–21:00 UTC Oct 3 05:00–06:00, 20:00–22:00 UTC Oct 4 05:00–06:00, 20:00–22:00 UTC Oct 5 06:00–07:00, 20:00–21:00 UTC Oct 6 05:00–06:00, 20:00–22:00 UTC Oct 7 20:00–22:00 UTC Oct 8 05:00–06:00, 20:00–22:00 UTC Oct 9 05:00–06:00 UTC Oct 10 20:00–21:00 UTC Oct 11 20:00–22:00 UTC Oct 12 05:00–06:00, 20:00–21:00 UTC Oct 13 05:00–06:00 UTC Oct 14 05:00–06:00 UTC Oct 17 20:00–23:00 UTC Oct 18 20:00–22:00 UTC Oct 19 20:00–22:00 UTC Oct 21 20:00–23:00 UTC Oct 22 17:00–22:00 UTC Oct 23 20:00–22:00 UTC Oct 24 20:00–22:00 UTC Oct 25 20:00–22:00 UTC Oct 26 20:00–22:00 UTC Oct 27 20:00–21:00 UTC Oct 28 20:00–21:00 UTC Oct 29 20:00–22:00 UTC Oct 30 20:00–22:00 UTC Oct 31 21:00–22:00 UTC
November
Nov 1 21:00–23:00 UTC Nov 2 21:00–22:00 UTC Nov 3 20:00–22:00 UTC Nov 4 19:00–23:00 UTC Nov 5 21:00–23:00 UTC Nov 6 21:00–23:00 UTC Nov 7 21:00–23:00 UTC Nov 8 18:00–20:00 UTC Nov 9 21:00–23:00 UTC Nov 10 17:00–18:00, 21:00–23:00 UTC Nov 11 21:00–23:00 UTC Nov 12 17:00–18:00, 21:00–23:00 UTC Nov 13 21:00–23:00 UTC Nov 14 21:00–22:00 UTC Nov 15 21:00–23:00 UTC Nov 16 21:00–22:00 UTC Nov 17 21:00–22:00 UTC Nov 18 21:00–22:00 UTC Nov 24 21:00–22:00 UTC Nov 25 20:00–22:00 UTC Nov 26 17:00–19:00 UTC Nov 29 00:00–01:00, 21:00–24:00 UTC Nov 30 20:00–21:00 UTC
December
Dec 1 17:00–18:00, 21:00–23:00 UTC Dec 2 22:00–23:00 UTC Dec 3 17:00–18:00, 21:00–23:00 UTC Dec 4 21:00–23:00 UTC Dec 5 21:00–22:00 UTC Dec 6 21:00–22:00 UTC Dec 7 21:00–22:00 UTC Dec 8 21:00–23:00 UTC Dec 10 22:00–24:00 UTC Dec 11 22:00–24:00 UTC Dec 12 16:00–17:00, 20:00–22:00 UTC Dec 13 17:00–18:00, 20:00–23:00 UTC Dec 14 20:00–22:00 UTC Dec 15 20:00–22:00 UTC Dec 16 16:00–17:00, 21:00–23:00 UTC Dec 17 21:00–23:00 UTC Dec 18 16:00–17:00, 21:00–23:00 UTC Dec 19 20:00–21:00 UTC Dec 20 16:00–18:00, 21:00–23:00 UTC Dec 21 18:00–20:00 UTC Dec 22 15:00–16:00 UTC Dec 23 16:00–17:00, 22:00–23:00 UTC Dec 26 21:00–23:00 UTC Dec 27 21:00–23:00 UTC Dec 28 18:00–20:00, 22:00–23:00 UTC Dec 29 16:00–18:00, 21:00–23:00 UTC Dec 30 21:00–23:00 UTC Dec 31 20:00–21:00 UTC