If you're talking gold, anytime is a good time IMO. It's been $1500 AUD in the past - look for 2, 3, 5 year graphs for an idea. Silver on the other hand is much more volatile and buying on an absolute spike like happened this week saw a pullback from $34 AUD to the low $32.39 AUD a day later. One day though it's just not going to have a pullback, so....