Croatian port getting support in a jiffy (5,6)
I believe the answer is:
split second
'jiffy' is the definition.
(synonyms)
'croatian port getting support' is the wordplay.
'croatian port' becomes 'split' (I've seen this before).
'getting' means one lot of letters go next to another.
'support' becomes 'second' (eg to second an idea is to support it).
'split'+'second'='SPLIT-SECOND'
'in a' acts as a link.
(Other definitions for split second that I've seen before include "Instant" , "Twinkling of an eye" , "An extremely short time" , "Very brief moment of time" , "Very little time" .)