If between the 1st of Jan and of Feb, there's little time (4)
I believe the answer is:
jiff
'little time' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'if between the 1st of jan and of feb' is the wordplay.
'between' indicates putting letters inside.
'the fst of jan' becomes 'j' (fst letter of 'jan').
'and' means one lot of letters go next to another.
'of feb' becomes 'f' (I can't justify this - if you can you should give a lot more credence to this answer).
'j'+'f'='jf'
'if' going within 'jf' is 'JIFF'.
'there's' acts as a link.
Can you help me to learn more?
(Other definitions for jiff that I've seen before include "Second" , "A mo" , "Two shakes" , "Instant (sl)" .)