Attentive porter possibly has right time (5)
I believe the answer is:
alert
'attentive' is the definition.
(I've seen this before)
'porter possibly has right time' is the wordplay.
'porter possibly' becomes 'ale' (porter is a kind of ale).
'has' says to put letters next to each other.
'right' becomes 'r' (abbreviation).
'time' becomes 't' (abbreviation).
'ale'+'r'+'t'='ALERT'
(Other definitions for alert that I've seen before include "Signal danger" , "Lively" , "Watchful, quick-thinking" , "Vigilantly attentive" , "'Attentive, watchful (5)'" .)