Customs taking a long time in American ship (6)
I believe the answer is:
usages
'customs' is the definition.
(I know this)
'a long time in american ship' is the wordplay.
'a long time' becomes 'age' (an age is a period of time).
'in' indicates putting letters inside.
'american ship' becomes 'USS' (United States Ship, prefix used in US ship names).
'age' inserted into 'uss' is 'USAGES'.
'taking' is the link.
(Other definitions for usages that I've seen before include "Habitual practices with words" , "Customary treatments, practices" , "Habitual or customary practices" , "Customs." , "speech patterns" .)