It’s apt to be hastily diminished (5)
I believe the answer is:
speed
'apt to be hastily diminished' is the definition.
I can't tell whether this definition defines the answer.
'it's' is the wordplay.
I cannot really see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is located in the answer.
The remaining letters 'sped' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for speed that I've seen before include "Move quickly (and illegally?)" , "Race" , "Rtae of progress" , "Film sensitivity to light" , "Hasten" .)