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 judge 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 am not sure about this - if you are sure 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" .)