In general, you should plan to launch the SSAT at Home 30 minutes prior to your scheduled time. This will allow you to log in to your SSAT account, launch the Secure Browser, and complete the room scan and selfie.
Similar to other appointments, your proctor and time slot have been reserved for you. It is possible to launch your SSAT at Home up to 15 minutes after your scheduled time. After this, unless you have already launched the test and are working with technical support or launched and are simply waiting for a proctor to join, your testing appointment will be canceled and unavailable.