Still interrupting other shop’s opening for a snack (9)
I believe the answer is:
elevenses
'for a snack' is the definition.
(I've seen this before)
'still interrupting other shop's opening' is the wordplay.
'still' becomes 'even' (synonyms).
'interrupting' indicates putting letters inside.
'other shop's opening' becomes 'elses' (I am not sure about this - if you are sure you should believe this answer much more).
'even' placed within 'elses' is 'ELEVENSES'.
Can you help me to learn more?
(Other definitions for elevenses that I've seen before include "energy getting second break" , "Mid-morning refreshment" , "Mid-morning snack" , "Mid-morning snacks" , "Morning refreshment break" .)