During time that one can remember explosive glimmer on ivy (6,6)
I believe the answer is:
living memory
'during time that one can remember' is the definition.
(I've seen this before)
'explosive glimmer on ivy' is the wordplay.
'explosive' indicates an anagram.
'glimmer'+'on'+'ivy'='glimmeronivy'
'glimmeronivy' with letters rearranged gives 'LIVING MEMORY'.
(Other definitions for living memory that I've seen before include "Time still recalled" , "During time that one can remember" .)