There are 3 kinds of feint buffer:
5 (1/3/4) 2/6 A+C
(1) The initial direction of the command is neutral. You remain on it as long as you like.
(2) But once you leave that initial direction of neutral for one frame of a direction that is not the 2 or 6 direction you have 7F to go to the 2 or 6 direction (8F total buffer).
(3) After the first frame of 2 or 6 direction, you have 8F to press A+C together to feint in that direction (9F total buffer).
5 6 A+C
5 6 2 A+C
(1) The initial direction of the command is neutral. You remain on it as long as you like.
(2) But once you leave that initial direction of neutral for one frame of the 6 direction,
you have 8F to press A+C together to forward feint (9F total buffer);
OR you have 7F to go to the 2 direction (8F total buffer).
(3) After the first frame of the 2 direction, you have 8F to press A+C together to down feint (9F total buffer).
5 2 A+C
5 2 6 A+C
(1) The initial direction of the command is neutral. You remain on it as long as you like.
(2) But once you leave that initial direction of neutral for one frame of the 2 direction,
you have 8F to press A+C together to down feint (9F total buffer);
OR you have 7F to go to the 6 direction (8F total buffer).
(3) After the first frame of the 6 direction, you have 8F to press A+C together to forward feint (9F total buffer). (If you press A+C before the down feint buffer ends you will still get the down feint.)
After the buffer is exceeded, you only need to go to at least 1 frame of neutral to reset the buffer before you redo the input.
At the start of the new buffer, you can't press the feint direction at the same time as A+C.