When the outside crumbles, hurry (5)
I believe the answer is:
haste
'hurry' is the definition.
(haste is hurrying or rushing)
'when the outside crumbles' is the wordplay.
I cannot quite see how this works, but
'when' could be 'as' (eg 'when I walked' means 'as I walked') and 'as' is found within the answer.
an anagram of 'the' is 'hte' which is present in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for haste that I've seen before include "Rash speed" , "Inconsiderate speed" , "Hurriedness" , "Leader abandons modest" , "Speediness or rush" .)