Composed of women, at that time lacking leader (3)
I believe the answer is:
hen
'composed of women' is the definition.
(as in a hen night)
'that time lacking leader' is the wordplay.
'that time' becomes 'when' (I've seen this before).
'lacking leader' means to remove the first letter.
'when' with its initial letter taken away is 'HEN'.
'at' acts as a link.
(Other definitions for hen that I've seen before include "Coop resident" , "Adult female chicken" , "Domestic egg layer" , "This party is for women only" , "Composed of women" .)