This is the actual site that virtual lab is run from. You can sign in about 10 minutes early so you are ready to go. You may sign in/out anytime during the 1 hour block (usually from 8pm to 9pm the night before a test).
You may also access the lab from the Griffin Lab Calendar. Just click on the subject you are looking for. There is a link for the calendar here or on the school website on the right side or under the "academics" tab.