Second to interrupt when showing book (4)
I believe the answer is:
amos
'book' is the definition.
(Old Testament book)
'second to interrupt when' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'to interrupt' indicates putting letters inside.
'when' becomes 'as'.
'mo' going within 'as' is 'AMOS'.
'showing' is the link.
(Other definitions for amos that I've seen before include "American wild dog" , "Biblical character" , "Old Testament book" , "man" , "Old Testament prophet" .)