Without delay: therefore one’s ahead of time (7)
I believe the answer is:
soonest
'without delay' is the definition.
Both the definition and answer are adverbs. Perhaps there's a link between them I don't understand?
'therefore one's ahead of time' is the wordplay.
'therefore' becomes 'so' ('so' can mean 'consequently' or 'therefore').
'ahead of' means one lot of letters go next to another (some letters go in front of others).
'time' becomes 't' (abbreviation).
'so'+'ones'+'t'='SOONEST'
Can you help me to learn more?
(Other definitions for soonest that I've seen before include "'Least said, ... mended (7)'" , "Most readily" , "As early as possible" , "At the earliest time" , "First" .)