Typically the judge asks if they are ready to begin before they start the clock.Having judged before, the teams that come in with simple props and streamlined set up are well positioned to perform (less nervous, rushed). Practicing set up as well as the skit will help.
The judging rubric can give your team a good idea of what the judges are looking for in terms of content and preparation.
Our team has found the rubric to be a great tool to self-assess before the tournament.
Also, you probably remember that your team must set up independently and leave the room as you found it (removing any debris generated during the skit, if any).
Co-Coach of The BrickBeasts