Call up the night before to gain permission (5)
I believe the answer is:
evoke
'call up' is the definition.
('evoke' can be a synonym of 'call up')
'the night before to gain permission' is the wordplay.
'the night before' becomes 'eve' (I've seen this before).
'to gain' means one lot of letters goes inside another.
'permission' becomes 'ok' (what is said to give permission).
'eve' enclosing 'ok' is 'EVOKE'.
(Other definitions for evoke that I've seen before include "Rekindle" , "Raise" , "Conjure up" , "Call to mind (memories)" , "Call up as from memory" .)