Made slow progress: stole quietly away (6)
I believe the answer is:
inched
'made slow progress' is the definition.
(as in to inch along slowly)
'stole quietly away' is the wordplay.
'stole' becomes 'pinched' (pinching is a kind of stealing).
'quietly' becomes 'p' (p for piano and quiet).
'away' is a deletion indicator.
'pinched' with 'p' removed is 'INCHED'.
(Other definitions for inched that I've seen before include "Moved by slow degrees" , "Moved along very slowly" , "Moved in small increments" , "Moved gradually" .)