Menu with quail: aunt ordered, given steer, some time in September (8,7)
I believe the answer is:
autumnal equinox
'some time in september' is the definition.
'menu with quail aunt ordered given steer' is the wordplay.
'with' is a charade indicator (letters next to each other).
'ordered' indicates an anagram.
'given' is a charade indicator (letters next to each other).
'steer' becomes 'ox' (a steer is a castrated ox).
'quail'+'aunt'='quailaunt'
'menu' put after 'quailaunt' is 'quailauntmenu'.
'quailauntmenu' with letters rearranged gives 'autumnalequin'.
'autumnalequin'+'ox'='AUTUMNAL EQUINOX'
(Another definition for autumnal equinox that I've seen is " one day in September? - with 21d".)