Timing stock sales and purchases is a constant trade-off between current and expected future prices, and current and expected future feed supply.
Aim to sell surplus stock (culls, cast for age) when the stock are still in good condition. Typically, this will be late spring or early summer in the south and late autumn in the north. In a good year, delay stock sales to improve pasture utilisation and animal liveweight at sale. In a bad year, bring stock sales forward to reduce stocking rate and conserve feed for other stock.
Similar flexibility can be applied to the timing of lamb sales and the target market, e.g., feeder, finished or hoggets.