An unspecified amount to overturn release eventually, although we don't know exactly when (8)
I believe the answer is:
sometime
'eventually although we don't know exactly when' is the definition.
I can't tell whether this definition defines the answer.
'an unspecified amount to overturn release' is the wordplay.
'an unspecified amount' becomes 'some' (I've seen this before).
'to overturn' shows that the letters should be reversed in order.
'release' becomes 'emit' (emitting is a kind of releasing).
'emit' written backwards gives 'time'.
'some'+'time'='SOMETIME'
Can you help me to learn more?
(Other definitions for sometime that I've seen before include "On an undetermined date in the future" , "One day" , "Former; occasional (US)" , "ex?" , "In the future, we don't know when" .)