Top ticket perhaps requiring time (7)
I believe the answer is:
singlet
'top' is the definition.
(I've seen this before)
'ticket perhaps requiring time' is the wordplay.
'ticket perhaps' becomes 'single'.
'requiring time' becomes 't' (I can't justify this - if you can you should give a lot more credence to this answer).
'single'+'t'='SINGLET'
Can you help me to learn more?
(Other definitions for singlet that I've seen before include "Tingles in vest" , "underclothing" , "Sleeveless shirt" , "Underwear" , "garment worn by men" .)