MC cable is allowed to be unsupported for 6' under these circumstances.
330.30(D)
(2) Is not more than 1.8 m (6 ft) in length from the last
point of cable support to the point of connection to
luminaires or other electrical equipment and the cable
and point of connection are within an accessible ceiling.
For the purpose of this section, Type MC cable
fittings shall be permitted as a means of cable support.
The same thing applies to AC cable. 320.30(D)(3).
Flex has such a rule, too. 348.30(A), Exception #4
There is no limit as to the length of supported cable or flex.
