Most often in March, 25 days.
Highest follower count seen that year: 9,169.
January
Jan 3 04:00–11:00 UTC Jan 5 05:00–10:00 UTC Jan 6 04:00–12:00 UTC Jan 8 04:00–12:00 UTC Jan 9 04:00–06:00, 08:00–12:00 UTC Jan 10 13:00–20:00 UTC Jan 12 12:00–19:00 UTC Jan 13 04:00–11:00 UTC Jan 14 04:00–12:00 UTC Jan 15 05:00–11:00 UTC Jan 17 05:00–12:00 UTC Jan 18 04:00–08:00 UTC Jan 19 04:00–12:00 UTC Jan 20 04:00–11:00 UTC Jan 21 04:00–12:00 UTC Jan 22 04:00–12:00 UTC Jan 24 05:00–12:00 UTC Jan 25 04:00–12:00 UTC Jan 26 04:00–11:00 UTC Jan 27 04:00–12:00 UTC Jan 28 03:00–08:00 UTC Jan 29 04:00–10:00 UTC Jan 30 04:00–08:00 UTC
February
Feb 4 03:00–06:00, 09:00–11:00 UTC Feb 5 04:00–08:00, 10:00–11:00 UTC Feb 6 03:00–11:00 UTC Feb 7 05:00–11:00 UTC Feb 8 04:00–05:00 UTC Feb 9 05:00–11:00 UTC Feb 10 04:00–10:00 UTC Feb 12 04:00–11:00 UTC Feb 13 04:00–12:00 UTC Feb 14 05:00–07:00, 09:00–11:00 UTC Feb 15 05:00–11:00 UTC Feb 16 04:00–11:00 UTC Feb 17 04:00–10:00 UTC Feb 18 04:00–10:00 UTC Feb 19 03:00–11:00 UTC Feb 21 04:00–11:00 UTC Feb 22 04:00–06:00 UTC Feb 23 04:00–11:00 UTC Feb 24 04:00–11:00 UTC Feb 25 05:00–11:00 UTC Feb 26 03:00–10:00 UTC Feb 28 04:00–11:00 UTC
March
Mar 2 04:00–11:00 UTC Mar 3 04:00–05:00, 07:00–11:00 UTC Mar 4 04:00–11:00 UTC Mar 5 05:00–11:00 UTC Mar 7 06:00–11:00 UTC Mar 8 05:00–11:00 UTC Mar 9 05:00–11:00 UTC Mar 10 04:00–11:00 UTC Mar 11 04:00–11:00 UTC Mar 13 03:00–11:00 UTC Mar 14 04:00–11:00 UTC Mar 15 05:00–11:00 UTC Mar 16 06:00–10:00 UTC Mar 17 03:00–11:00 UTC Mar 18 03:00–11:00 UTC Mar 19 04:00–11:00 UTC Mar 21 04:00–11:00 UTC Mar 22 04:00–11:00 UTC Mar 23 04:00–11:00 UTC Mar 25 04:00–11:00 UTC Mar 26 05:00–11:00 UTC Mar 28 03:00–11:00 UTC Mar 29 07:00–12:00 UTC Mar 30 05:00–11:00 UTC Mar 31 04:00–10:00 UTC
April
Apr 1 05:00–11:00 UTC Apr 2 05:00–11:00 UTC Apr 3 04:00–10:00 UTC Apr 6 04:00–11:00 UTC Apr 7 04:00–11:00 UTC Apr 8 06:00–11:00 UTC Apr 9 04:00–10:00 UTC Apr 11 04:00–11:00 UTC Apr 12 04:00–11:00 UTC Apr 13 04:00–11:00 UTC Apr 14 04:00–10:00 UTC Apr 15 06:00–11:00 UTC Apr 16 04:00–11:00 UTC Apr 18 04:00–11:00 UTC Apr 20 06:00–12:00 UTC Apr 21 04:00–12:00 UTC Apr 22 06:00–11:00 UTC Apr 23 04:00–11:00 UTC Apr 26 06:00–11:00 UTC Apr 28 04:00–11:00 UTC Apr 29 03:00–06:00, 08:00–11:00 UTC Apr 30 04:00–11:00 UTC
May
May 2 03:00–05:00, 07:00–11:00 UTC May 5 04:00–12:00 UTC May 6 04:00–11:00 UTC May 7 04:00–11:00 UTC May 8 05:00–11:00 UTC May 11 04:00–12:00 UTC May 12 04:00–11:00 UTC May 13 03:00–11:00 UTC May 15 04:00–11:00 UTC May 16 06:00–11:00 UTC May 18 05:00–12:00 UTC May 19 05:00–11:00 UTC May 20 05:00–11:00 UTC May 21 05:00–12:00 UTC May 23 04:00–11:00 UTC May 24 04:00–08:00 UTC May 26 04:00–11:00 UTC May 27 04:00–11:00 UTC May 28 04:00–12:00 UTC May 29 04:00–11:00 UTC May 30 04:00–12:00 UTC May 31 05:00–06:00 UTC
June
Jun 2 04:00–12:00 UTC Jun 3 04:00–11:00 UTC Jun 4 04:00–11:00 UTC Jun 5 05:00–12:00 UTC Jun 9 04:00–12:00 UTC Jun 10 05:00–12:00 UTC Jun 11 04:00–11:00 UTC Jun 13 05:00–11:00 UTC Jun 15 03:00–12:00 UTC Jun 16 03:00–11:00 UTC Jun 17 04:00–12:00 UTC Jun 18 04:00–11:00 UTC Jun 20 04:00–12:00 UTC Jun 21 03:00–10:00 UTC Jun 22 04:00–11:00 UTC Jun 23 05:00–11:00 UTC Jun 24 06:00–12:00 UTC Jun 25 04:00–12:00 UTC Jun 26 02:00–12:00 UTC Jun 27 02:00–06:00 UTC Jun 30 05:00–10:00 UTC
July
Jul 1 03:00–12:00 UTC Jul 2 05:00–12:00 UTC Jul 3 06:00–12:00 UTC Jul 4 06:00–09:00 UTC Jul 6 05:00–11:00 UTC Jul 7 04:00–12:00 UTC Jul 8 04:00–12:00 UTC Jul 9 04:00–12:00 UTC Jul 10 05:00–12:00 UTC Jul 11 05:00–11:00 UTC Jul 12 04:00–10:00 UTC Jul 13 04:00–12:00 UTC Jul 14 04:00–07:00, 09:00–11:00 UTC Jul 15 08:00–09:00 UTC Jul 16 06:00–12:00 UTC Jul 18 07:00–12:00 UTC Jul 19 04:00–12:00 UTC Jul 20 04:00–10:00 UTC Jul 21 07:00–08:00 UTC Jul 22 03:00–11:00 UTC Jul 23 06:00–11:00 UTC Jul 25 04:00–05:00 UTC Jul 26 03:00–04:00 UTC Jul 27 05:00–10:00 UTC