Useful feature to order any time (7)
I believe the answer is:
Here is my best explanation:
'useful feature' is the definition.
(I've seen this before)
'order any time' is the subsidiary indication.
'order' indicates anagramming the letters.
'anytime' with letters rearranged gives 'amenity'.
'to' is the link.
(Other definitions for amenity that I've seen before include "Item provided to make life easier", "Facility, useful feature", "Any time for convenience or pleasentness", "Library perhaps", "Anytime (anag.)", "Facility serving the public", "Pleasing feature (of a place or building)", "Feature of place that makes living pleasant and convenient", "Feature of place that makes life easy or pleasant" and "Any item (anag.)".)