More spartan with time to negotiate (6)
I believe the answer is:
barter
'negotiate' is the definition.
(bartering is a kind of negotiating)
'more spartan with time' is the wordplay.
'more spartan' becomes 'barer' (I've seen this in another clue).
'with' indicates putting letters inside.
'time' becomes 't' (abbreviation).
'barer' going around 't' is 'BARTER'.
'to' acts as a link.
(Other definitions for barter that I've seen before include "Exchange, bargain" , "Trade or swap" , "Trade without using money" , "Trade, haggle" , "Give (goods) in exchange" .)