Boris partying limits time in restaurant (6)
I believe the answer is:
bistro
'restaurant' is the definition.
(I know that bistro is a type of restaurant)
'boris partying limits time' is the wordplay.
'partying' indicates anagramming the letters (I've seen 'parties' mean this (the letters move or party around)).
'limits' means one lot of letters goes inside another (limit can mean to contain or block off).
'time' becomes 't' (abbreviation).
'boris' with letters rearranged gives 'bisro'.
'bisro' enclosing 't' is 'BISTRO'.
'in' acts as a link.
(Other definitions for bistro that I've seen before include "family concern perhaps" , "Eating place" , "Small French bar and restaurant" , "Cafe bar" , "Small restaurant - robs it (anag)" .)