Fancy whistle -- end of time in short (4,5)
I believe the answer is:
pipe dream
'fancy' is the definition.
'whistle end of time in short' is the wordplay.
'whistle' becomes 'pipe' (I've seen this before).
'end of time in short' becomes 'dream' (I can't explain this - if you can you should give a lot more credence to this answer).
'pipe'+'dream'='PIPE-DREAM'
Can you help me to learn more?
(Other definitions for pipe dream that I've seen before include "Fantastic but vain hope" , "Unattainable hope" , "Fanciful hope" , "Sherlock's flight of fancy" , "castle in Spain?" .)