A long time getting back from the rose garden (4)
I believe the answer is:
ages
'a long time' is the definition.
(ages can mean a very long time)
'back from the rose garden' is the wordplay.
'back' is a reversal indicator.
'from' indicates a hidden word.
'sega' is hidden within 'rose garden'.
'sega' reversed gives 'AGES'.
'getting' acts as a link.
(Other definitions for ages that I've seen before include "... of Man, according to WB Yeats" , "Donkey's years" , "Epochs" , "Rock of - - (hymn)" , "Matures" .)