You can place a buy order with funds from the sale proceeds of your shares as soon as the sell trade has been booked to your order.
Buy orders can only be placed if you have sufficient cleared funds in your Direct Investment Account as stocks cannot be used as collateral.
However, you can sell shares and use the sale proceeds to buy shares immediately after the transaction has been completed on the market.
Sale proceeds must have settled before they can be made available for any purposes other than trading.