Confirm I had a brief time in glen (8)
I believe the answer is:
validate
'confirm' is the definition.
(validating is a kind of confirming)
'i had a brief time in glen' is the wordplay.
'i had' becomes 'id' (I'd).
'brief time' becomes 't' (I am not sure about the 'brief' bit.**).
'in' means one lot of letters goes inside another.
'glen' becomes 'vale' (I've seen this in other clues).
'id'+'a'+'t'='idat'
'idat' going within 'vale' is 'VALIDATE'.
Can you help me to learn more?
(Other definitions for validate that I've seen before include "Confirm truth of (item)" , "Certify or authenticate" , "Prove" , "Confirm as true" , "Confirm correctness of" .)