Important time to plug bottle (5)
I believe the answer is:
vital
'important' is the definition.
(I know that important can be written as vital)
'time to plug bottle' is the wordplay.
'time' becomes 't' (abbreviation).
'to plug' means one lot of letters goes inside another (to plug can mean to block a gap within something).
'bottle' becomes 'vial' (vial is a kind of bottle).
't' inserted within 'vial' is 'VITAL'.
(Other definitions for vital that I've seen before include "Urgently needed or absolutely necessary" , "Essential to life, indispensable" , "Critical, necessary" , "Imperative" , "alive" .)