Case modified after usual time to increase in intensity (8)
I believe the answer is:
escalate
'increase in intensity' is the definition.
(I've seen this before)
'case modified after usual time' is the wordplay.
'modified' is an anagram indicator.
'after usual time' becomes 'late' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'case' anagrammed gives 'esca'.
'esca'+'late'='ESCALATE'
'to' is the link.
Can you help me to learn more?
(Other definitions for escalate that I've seen before include "Amplify" , "Magnify" , "Raise to higher level, perhaps war" , "Rapidly increase in intensity" , "Tease Cal badly and mount up" .)