No, not as soon as they are placed. When the automatic import option is enabled on your store, ShipStation makes periodic calls to the selling channel to request orders. This option is enabled by default for all stores, and can be found in each store's Store Settings tab.
The interval between these requests is based on an algorithm and is determined by a number of factors including the volume of orders imported from the store. At this time, automatic imports cannot be scheduled or customized.
You can also manually initiate order imports any time you like by clicking the import button in your ShipStation toolbar.