When working on your lab, you will see a Time Remaining counter at the top right of the window.


Labs are designed to be run in the specified time of the lab, from start to end. Once the lab is closed, your progress is cleared, and data reset to its base state.


If you are returning to a lab after partially completing it, you will need to begin from the first step again, carefully following all directions.


Related: 

Can I save or export my working files?