It will take the ATO 24-48 following successful registration to upload your ABN details to the ABR website, including the specific ABN lookup.
You have the chance to select an ABN start date in your application. Should you choose a future date, your ABN details will not appear on the ABR website until this date. However you may receive an email prior to this date, stating that your ABN has been registered. It WILL NOT be active until the date specified in the ABN application.