Answer
Whenever your buy or sell order has been filled, the transaction has to go through various steps of what's known as the 'custody chain' before it is completed. Below, you'll find a step-by-step description of the process from placing an order to completion of the transaction.
However, you do not have to wait for this process before anything changes in your account. Upon receipt of the transaction confirmation, the positions in your account will be updated and you will be free to place another order in the same product.