Hide as soon as having entered state (7)
I believe the answer is:
conceal
'hide' is the definition.
(I know that hide can be written as conceal)
'as soon as having entered state' is the wordplay.
I cannot quite see how this works, but
'as soon as' could be 'once' (once can mean immediately after) and 'once' is found in the answer.
'state' could be 'cal' (short for California) and 'cal' is found in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for conceal that I've seen before include "Screen" , "Hide, cover" , "Keep out of sight" , "Place out of sight" , "'Hide, keep secret (7)'" .)