Walk past bar when on time (6)
I believe the answer is:
prompt
'on time' is the definition.
(synonyms)
'walk past bar when' is the wordplay.
'walk' becomes 'prom' (I have seen 'Short walk' mean 'prom' so perhaps 'walk' could also mean 'prom').
'bar' indicates named letters should be taken away ('bar' can mean 'except' or 'apart from').
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'past' with 'as' taken out is 'pt'.
'prom'+'pt'='PROMPT'
(Other definitions for prompt that I've seen before include "Jog the memory" , "Ready" , "Cue; punctual" , "Remind (actor) of lines" , "Whisper line to forgetful actor" .)