Walk over: time to pick up a book (5)
I believe the answer is:
tread
'walk over' is the definition.
'time to pick up a book' is the wordplay.
'time' becomes 't'.
'to pick up a book' becomes 'read'.
't'+'read'='TREAD'
(Other definitions for tread that I've seen before include "Top surface of a stair step" , "A measurement of tyre" , "Grooved surface of a tyre" , "March" , "Walk or step like pattern on tyre" .)