March Ides essentially, short time (4)
I believe the answer is:
demo
'march' is the definition.
(as in a demonstration)
'ides essentially short time' is the wordplay.
'essentially' indicates the central letters.
'short time' becomes 'mo' (as in 'just a mo').
The middle of 'ides' is 'de'.
'de'+'mo'='DEMO'
(Other definitions for demo that I've seen before include "Eg, protest march" , "exhibit" , "Tape sent to recording studio" , "illustration" , "In brief, a public event as of protest under dome" .)