Within the validity period. (e.g. Within the validity of the ticket).
You can leave and re-enter Australia any number of times while the visa is valid. (pode-se entrar na Austrália quantas vezes quiser, dentro da validade do visto).
In Canada, for instance, there are "best before" and "expire dates", if you consume food with a "best before" label (and within that date), you know that the full nutrients are as outlined on the label.
Within expire-date it is not that fresh, but you still can consume.