Would have you believe, before time is up (8)
I believe the answer is:
pretends
'would have you believe' is the definition.
I can't tell whether this defines the answer.
'before time is up' is the wordplay.
'before' becomes 'pre' (prefix meaning 'before').
'time' becomes 't' (abbreviation).
'is up' becomes 'ends' (I can't justify this - if you can you should give a lot more credence to this answer).
'pre'+'t'+'ends'='PRETENDS'
Can you help me to learn more?
(Other definitions for pretends that I've seen before include "Affects" , "Feigns, dissembles" , "poses" , "Creates false appearance or impression" , "Lays claim" .)