The absolute worst thing about prescreens is that a lot of schools have time requirements for monologues and songs. Typically, they are within the 60-90 second range, and sometimes schools even have the slates included in that time, so the pressure is definitely on for those performances. 

I cannot lie to you, timing your pieces sucks, especially if you have a monologue you love. My advice for this is to time them before you start filming. Take a timer and just go through the monologue as you would normally, because rushing will be your enemy. After you finish, check how long it took. If it’s over that 60-90 second mark, you will need to start cutting lines. This is particularly hard with Shakespeare's monologues and other classical pieces, but I promise, you will survive. 

If you have a piece that seems impossible to cut, however, you might have to part with it for prescreens, but be comforted in the fact that you could potentially use it for in-person auditions since those usually are more lenient with time limits, but it’s different for every school. Just go through trial and error and see what works and what doesn’t, and in the end, it’ll be worth it because you won’t have to rush through your pieces just to fit that time constraint.