Most often in March, 27 days.
Highest follower count seen that year: 11,722.
February
Feb 6 02:00–07:00, 10:00–11:00, 13:00–16:00 UTC Feb 7 03:00–16:00 UTC Feb 8 04:00–07:00, 09:00–15:00 UTC Feb 9 02:00–07:00, 09:00–15:00 UTC Feb 10 03:00–07:00, 10:00–15:00 UTC Feb 11 02:00–08:00, 10:00–15:00 UTC Feb 12 02:00–13:00 UTC Feb 13 02:00–07:00, 09:00–14:00 UTC Feb 14 02:00–07:00, 09:00–17:00 UTC Feb 15 02:00–07:00, 09:00–14:00 UTC Feb 16 02:00–07:00, 10:00–15:00 UTC Feb 17 02:00–15:00 UTC Feb 18 02:00–07:00, 10:00–15:00 UTC Feb 19 02:00–07:00, 09:00–15:00 UTC Feb 20 02:00–07:00, 09:00–15:00 UTC Feb 21 02:00–05:00, 13:00–17:00 UTC Feb 22 02:00–07:00, 09:00–16:00 UTC Feb 23 03:00–07:00, 09:00–16:00 UTC Feb 24 02:00–07:00, 09:00–15:00 UTC Feb 25 02:00–07:00, 09:00–16:00 UTC Feb 26 02:00–16:00 UTC Feb 27 02:00–07:00 UTC Feb 28 08:00–15:00 UTC
March
Mar 1 04:00–08:00, 10:00–15:00 UTC Mar 2 02:00–07:00, 09:00–15:00 UTC Mar 3 02:00–07:00, 09:00–15:00 UTC Mar 4 02:00–07:00, 10:00–16:00 UTC Mar 5 02:00–07:00, 09:00–15:00 UTC Mar 6 02:00–07:00, 09:00–16:00 UTC Mar 7 02:00–07:00, 09:00–16:00 UTC Mar 8 02:00–07:00, 09:00–15:00 UTC Mar 9 02:00–07:00, 09:00–16:00 UTC Mar 10 02:00–07:00, 09:00–15:00 UTC Mar 11 02:00–07:00, 09:00–16:00 UTC Mar 12 03:00–15:00 UTC Mar 13 03:00–07:00, 09:00–16:00 UTC Mar 14 02:00–07:00, 09:00–16:00 UTC Mar 15 02:00–07:00, 09:00–15:00 UTC Mar 16 02:00–07:00, 09:00–15:00 UTC Mar 17 02:00–07:00, 09:00–15:00 UTC Mar 18 02:00–07:00, 09:00–15:00 UTC Mar 23 02:00–15:00 UTC Mar 24 02:00–07:00, 09:00–15:00 UTC Mar 25 02:00–07:00, 09:00–16:00 UTC Mar 26 02:00–07:00, 09:00–15:00 UTC Mar 27 02:00–06:00 UTC Mar 28 02:00–07:00, 10:00–15:00 UTC Mar 29 02:00–06:00, 17:00–21:00 UTC Mar 30 02:00–07:00, 09:00–15:00 UTC Mar 31 02:00–07:00, 09:00–14:00 UTC
April
Apr 1 02:00–07:00, 09:00–15:00 UTC Apr 2 02:00–07:00, 09:00–15:00 UTC Apr 3 02:00–07:00, 09:00–15:00 UTC Apr 4 02:00–07:00, 09:00–15:00 UTC Apr 5 03:00–08:00, 10:00–15:00 UTC Apr 6 02:00–07:00, 09:00–15:00 UTC Apr 7 03:00–07:00, 09:00–15:00 UTC Apr 8 02:00–16:00 UTC Apr 9 02:00–15:00 UTC Apr 10 02:00–07:00, 09:00–14:00 UTC Apr 11 03:00–07:00, 09:00–15:00 UTC Apr 12 02:00–07:00, 09:00–15:00 UTC Apr 13 02:00–06:00, 09:00–15:00 UTC Apr 14 02:00–15:00 UTC Apr 15 02:00–15:00 UTC Apr 16 02:00–07:00, 10:00–16:00 UTC Apr 17 02:00–07:00, 09:00–15:00 UTC Apr 18 02:00–07:00, 09:00–15:00 UTC Apr 23 02:00–07:00, 10:00–15:00 UTC Apr 24 02:00–07:00, 09:00–15:00 UTC Apr 25 02:00–07:00, 09:00–15:00 UTC Apr 26 02:00–07:00, 15:00–21:00 UTC Apr 27 02:00–15:00 UTC Apr 28 02:00–16:00 UTC Apr 29 02:00–15:00 UTC Apr 30 03:00–07:00, 09:00–15:00 UTC
May
May 1 02:00–07:00, 09:00–14:00, 23:00–24:00 UTC May 2 00:00–05:00, 09:00–13:00 UTC May 3 00:00–06:00, 09:00–14:00, 23:00–24:00 UTC May 4 00:00–05:00, 08:00–13:00, 23:00–24:00 UTC May 5 00:00–05:00, 08:00–13:00 UTC May 6 00:00–07:00, 09:00–14:00, 23:00–24:00 UTC May 7 00:00–05:00 UTC