Time to be served unknown but flexible (8)
I believe the answer is:
stretchy
'flexible' is the definition.
(synonyms)
'time to be served unknown' is the wordplay.
'time' becomes 'stretch' (I've seen this before).
'to be served unknown' becomes 'y' (I can't justify this - if you can you should give a lot more credence to this answer).
'stretch'+'y'='STRETCHY'
'but' is the link.
Can you help me to learn more?
(Other definitions for stretchy that I've seen before include "Flexible" , "Of variable length, perhaps" , "Elastic" .)