Weight on silver point? That's a long time ago (8)
I believe the answer is:
stoneage
'a long time ago' is the definition.
I can't judge whether this defines the answer.
'weight on silver point?' is the wordplay.
'weight' becomes 'stone' (stone is a unit of weight).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'point?' becomes 'E' (compass point).
'stone'+'ag'+'e'='STONEAGE'
'that's' acts as a link.
Can you help me to learn more?
(Another definition for stoneage that I've seen is " long, long ago".)