Most often in June, 28 days.
Highest follower count seen that year: 2,350.
March
Mar 6 22:00–23:00 UTC Mar 7 00:00–03:00 UTC Mar 8 21:00–24:00 UTC Mar 9 00:00–02:00, 21:00–24:00 UTC Mar 10 00:00–02:00, 21:00–24:00 UTC Mar 11 00:00–03:00, 20:00–24:00 UTC Mar 12 00:00–03:00, 20:00–24:00 UTC Mar 13 00:00–03:00, 20:00–24:00 UTC Mar 14 00:00–03:00 UTC Mar 16 20:00–24:00 UTC Mar 17 00:00–02:00, 21:00–23:00 UTC Mar 18 00:00–02:00, 20:00–24:00 UTC Mar 19 00:00–03:00, 21:00–24:00 UTC Mar 20 00:00–02:00, 21:00–24:00 UTC Mar 21 00:00–03:00 UTC Mar 22 20:00–24:00 UTC Mar 23 00:00–03:00 UTC Mar 24 20:00–24:00 UTC Mar 25 00:00–02:00, 20:00–24:00 UTC Mar 26 00:00–02:00, 21:00–24:00 UTC Mar 27 00:00–03:00, 18:00–24:00 UTC Mar 29 21:00–24:00 UTC Mar 30 00:00–12:00, 18:00–24:00 UTC Mar 31 00:00–01:00 UTC
April
Apr 1 00:00–02:00, 22:00–24:00 UTC Apr 2 00:00–03:00, 20:00–24:00 UTC Apr 3 00:00–02:00 UTC Apr 5 20:00–24:00 UTC Apr 6 00:00–02:00, 21:00–24:00 UTC Apr 7 00:00–01:00, 04:00–11:00, 20:00–24:00 UTC Apr 8 00:00–02:00, 22:00–24:00 UTC Apr 9 00:00–02:00 UTC Apr 10 21:00–22:00 UTC Apr 12 20:00–24:00 UTC Apr 13 00:00–03:00, 21:00–24:00 UTC Apr 14 00:00–01:00, 21:00–24:00 UTC Apr 15 00:00–02:00, 17:00–24:00 UTC Apr 16 00:00–02:00, 04:00–10:00, 20:00–24:00 UTC Apr 17 00:00–02:00, 20:00–24:00 UTC Apr 18 00:00–02:00, 21:00–24:00 UTC Apr 19 00:00–02:00, 20:00–24:00 UTC Apr 20 00:00–02:00, 04:00–06:00 UTC Apr 21 20:00–24:00 UTC Apr 22 00:00–02:00, 20:00–24:00 UTC Apr 23 00:00–02:00, 21:00–24:00 UTC Apr 24 00:00–02:00, 21:00–24:00 UTC Apr 25 00:00–03:00 UTC Apr 26 21:00–23:00 UTC Apr 27 00:00–03:00, 21:00–24:00 UTC Apr 28 00:00–02:00 UTC Apr 29 19:00–23:00 UTC Apr 30 00:00–02:00, 20:00–24:00 UTC
May
May 1 00:00–03:00, 21:00–24:00 UTC May 2 00:00–03:00 UTC May 3 00:00–03:00, 21:00–24:00 UTC May 4 00:00–02:00, 05:00–08:00 UTC May 5 21:00–24:00 UTC May 6 00:00–02:00, 21:00–24:00 UTC May 7 00:00–02:00 UTC May 8 21:00–24:00 UTC May 9 00:00–01:00 UTC May 10 20:00–24:00 UTC May 11 00:00–09:00, 21:00–24:00 UTC May 12 00:00–01:00, 21:00–24:00 UTC May 13 00:00–08:00, 20:00–24:00 UTC May 14 00:00–02:00, 22:00–24:00 UTC May 17 20:00–24:00 UTC May 18 00:00–01:00 UTC May 20 05:00–06:00, 20:00–22:00 UTC May 21 01:00–09:00, 21:00–24:00 UTC May 22 00:00–01:00, 21:00–24:00 UTC May 23 00:00–04:00 UTC May 25 21:00–24:00 UTC May 26 00:00–06:00, 21:00–24:00 UTC May 27 00:00–02:00 UTC May 28 04:00–10:00, 21:00–24:00 UTC May 29 00:00–02:00, 21:00–24:00 UTC May 30 00:00–03:00 UTC May 31 20:00–24:00 UTC
June
Jun 1 00:00–02:00, 21:00–24:00 UTC Jun 2 00:00–02:00, 21:00–24:00 UTC Jun 3 00:00–03:00, 21:00–24:00 UTC Jun 4 00:00–08:00, 22:00–24:00 UTC Jun 5 00:00–03:00, 21:00–24:00 UTC Jun 6 00:00–04:00 UTC Jun 7 22:00–24:00 UTC Jun 8 01:00–03:00, 21:00–24:00 UTC Jun 9 00:00–08:00, 21:00–24:00 UTC Jun 10 00:00–03:00, 05:00–10:00 UTC Jun 11 20:00–24:00 UTC Jun 12 00:00–03:00, 22:00–24:00 UTC Jun 13 00:00–03:00 UTC Jun 15 20:00–24:00 UTC Jun 16 00:00–01:00 UTC Jun 17 16:00–24:00 UTC Jun 18 21:00–24:00 UTC Jun 19 00:00–01:00, 20:00–24:00 UTC Jun 20 00:00–01:00 UTC Jun 21 20:00–24:00 UTC Jun 22 00:00–02:00, 04:00–10:00, 18:00–24:00 UTC Jun 23 00:00–01:00 UTC Jun 24 21:00–24:00 UTC Jun 25 00:00–01:00 UTC Jun 26 20:00–24:00 UTC Jun 27 00:00–03:00, 20:00–24:00 UTC Jun 29 20:00–24:00 UTC Jun 30 00:00–02:00, 04:00–10:00, 22:00–24:00 UTC
July
Jul 1 00:00–02:00, 21:00–24:00 UTC Jul 2 00:00–03:00, 20:00–24:00 UTC Jul 3 00:00–01:00 UTC Jul 4 20:00–24:00 UTC Jul 5 00:00–03:00, 20:00–24:00 UTC Jul 6 00:00–01:00, 21:00–24:00 UTC Jul 7 00:00–09:00, 21:00–24:00 UTC Jul 8 00:00–02:00 UTC Jul 9 22:00–24:00 UTC Jul 10 00:00–09:00, 18:00–24:00 UTC Jul 11 00:00–01:00 UTC Jul 12 21:00–24:00 UTC Jul 13 00:00–08:00, 21:00–24:00 UTC Jul 14 00:00–02:00, 21:00–24:00 UTC Jul 15 00:00–03:00, 08:00–11:00, 22:00–24:00 UTC Jul 16 00:00–03:00, 21:00–24:00 UTC Jul 17 00:00–02:00, 21:00–24:00 UTC Jul 18 01:00–09:00 UTC Jul 19 21:00–24:00 UTC Jul 20 00:00–07:00, 22:00–24:00 UTC Jul 21 00:00–01:00 UTC Jul 22 21:00–24:00 UTC Jul 23 01:00–08:00, 23:00–24:00 UTC Jul 24 00:00–05:00 UTC Jul 26 21:00–24:00 UTC Jul 27 00:00–02:00 UTC