A memo about time I had invested in cure (8)
I believe the answer is:
antidote
'cure' is the definition.
(I know that antidote is a type of cure)
'a memo about time i had invested' is the wordplay.
'memo' becomes 'note' (I've seen this before).
'about' indicates putting letters inside.
'time' becomes 't' (abbreviation).
'i had' becomes 'I'd' (contraction).
'invested' indicates putting letters inside.
'note' going around 't' is 'ntote'.
'ntote' going around 'id' is 'ntidote'.
'a'+'ntidote'='ANTIDOTE'
'in' acts as a link.
(Other definitions for antidote that I've seen before include "Medicine countering a poison" , "Agent counteracting a poison" , "Counter-agent" , "Counteractive medicine" , "Counter-measure" .)