once in a blue moon	very infrequently
allhis born days	all his life
in a mo/ in a sec/ in a tick/ in less than no time/ in a jiffy	very soon
for yonks/ for donkey's years/ since the year dot	for a long time
till the cows come home/ till hell freezes over	forever
for keeps	to keep forever
in the nick of time	only just in time
over the hill/ past it	too old
has-been	person who is no longer famous
in a flash/ at a rate of knots	very quickly
fleeting (glimpse/smile/visit)	brief or quick
transient (effect/population/feeling)	lasting for only a short time
persistent (cough/problems/rumour)	lasting for a long time or hard to stop
inexorable (rise/slide/decline)	continuing without hope of being stopped
incipient (frustration/rage/wrinkles)	just beginning
pristine (condition/beach/image)	unchanged from its original condition
protracted (negotiations/discussions/argument)	lasting for a long time or made to last longer
lingering (perfume/kiss/smile)	taking a long time to leave or disappear