Secrete at one time in California (7)
I believe the answer is:
conceal
'secrete' is the definition.
(I know that conceal is a is a kind of of secrete)
'one time in california' is the wordplay.
'one time' becomes 'once' (synonyms).
'in' means one lot of letters goes inside another.
'california' becomes 'cal' (short for California).
'once' placed within 'cal' is 'CONCEAL'.
'at' is the link.
(Other definitions for conceal that I've seen before include "Place out of sight" , "hush up!" , "Screen" , "Keep out of sight" , "'Hide, keep secret (7)'" .)