Now and then carpet empty library as befits it? (5)
I believe the answer is:
aptly
'as befits it?' is the definition.
(in a fitting or apt manner)
'now and then carpet empty library' is the wordplay.
'now and then' means one should take alternating letters (letters taken on a regular basis, now and then).
'empty' suggests removing the centre.
'library' with its centre taken out is 'ly'.
The alternating letters of 'carpet' are 'apt'.
'apt'+'ly'='APTLY'
(Other definitions for aptly that I've seen before include "In an appropriate way" , "In a competent manner" , "In suitable fashion" , "Appropriately" , "Suitably" .)