What Midas was given, extremely sensibly hidden, so long ago (7,5)
I believe the answer is:
donkeys years
'so long ago' is the definition.
(donkey's years can mean a very long time)
'what midas was given extremely sensibly hidden' is the wordplay.
'what midas was given' becomes 'donkeyears' (reference to Midas, figure of Greek myth).
'extremely' suggests removing the centre.
'hidden' means one lot of letters goes inside another.
'sensibly' with its centre removed is 'sy'.
'donkeyears' going around 'sy' is 'DONKEYS YEARS'.
(Other definitions for donkeys years that I've seen before include "Ages" , "A beastly long time" , "Yonks" , "An age" , "A long time (spent on Blackpool beach?)" .)