Essentially miserable time? (3)
I believe the answer is:
era
'time?' is the definition.
(era is a kind of time)
'essentially miserable' is the wordplay.
'essentially' says the answer is hidden in the clue (essence can mean the inside of something).
'ERA' is hidden in the letters of 'miserable'.
(Other definitions for era that I've seen before include "Important historical period" , "day" , "Characteristic period" , "Series of years" , "quite some time" .)