Time to pay bills from American: one retaining any number (6)
I believe the answer is:
usance
'time to pay' is the definition.
(I've seen this before)
'american one retaining any number' is the wordplay.
'american' becomes 'US' (United States).
'one' becomes 'ace' (ace has a value of one in some card games).
'retaining' means one lot of letters goes inside another (inserted letters are held or retained).
'any number' becomes 'n' (mathematical symbol for an unspecified number).
'ace' placed around 'n' is 'ance'.
'us'+'ance'='USANCE'
'bills from' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for usance that I've seen before include "time to settle" , "time for payment" , "practice" , "Usage (archaic)" , "interest in literature" .)