Tiny tree developing all the time (8)
I believe the answer is:
eternity
'all the time' is the definition.
(I've seen this before)
'tiny tree developing' is the wordplay.
'developing' indicates an anagram (letters developed into a new form).
'tiny'+'tree'='tinytree'
'tinytree' is an anagram of 'ETERNITY'.
(Other definitions for eternity that I've seen before include "Wolfgang Amadeus -" , "Hereafter" , "Endless time" , "Ages and ages" , "the poet palmed in an hour?" .)