What's the duration of time you have for each pitch session? Some of the fests are timed with stopwatches (five minute pitches) - others are more leisurely. But there will surely be a time limit. If you don't know how much time you have with each producer (executive, manager), find out. And figure it out from there.
You want to spend a percentage of your time chatting up the person. Personalization is important. Likability is a factor. Rushing in and starting the pitch isn't advised. Have a brief conversation. You want to be remembered as a person - not a pitcher. View the event as a networking opportunity. Be human. If someone likes you, they will remember you. They will be more inclined to return your emails or phone calls in the future. 5-10% of your time on casual conversation wouldn't hurt, IMO.
You'll want to spend 75-80% of your time on your pitch. The rest of your time should be reserved for feedback. It's a waste of time not to get some feedback from the person - to learn what's working or not working in the pitch, and/or on your pitch performance. This will enable you to fine tune the pitch throughout the day.
If you have the choice of scheduling your pitches, start the day with the least important people and hold off - until later in the day - the people you're dying to pitch most, because your pitch will get better.
Remember to PITCH your story - DON'T TELL IT. You're only presenting the broad strokes of the story. Do not get into the weeds.
Start off with the genre and logline. Then go into the broadstrokes of the story - beginning, middle, and end. Most people run out of time because they get sidetracked with story elements that are unnecessary for a pitch. It's important to know what to use and what to leave out for the purpose of a pitch. You are NOT telling the story from fade in to fade out. Not in this kind of pitch fest setting.
As a guideline, if your script is character driven - lead with the protagonist and then talk about the story. If the script is concept driven, lead with the story and then talk about the protagonist. When talking about your protagonist, consider how s/he dovetails with the drama and how s/he changes (their character arc).
Because it can be difficult to follow character names in a pitch, you could assign a movie star to the character.
You could say something like,"Mary Smith is a nurse, who works at a hospital. Think Viola Davis. When Viola spies a doctor stealing morphine...."
Viola will be more memorable to the listener than Mary. Remember, your listener is hearing one pitch after the other, and they all start to sound like one big story after a while. You need to present your story in the clearest way possible to the listener. You want to make it easy for the listener to follow and comprehend.
I've heard hundreds of thousands of pitches in 30 years, and most of them go off the rails because they get too detailed, complicated, and confusing.
If the story is told in a non-linear way, it might be best to give the listener that information up front, but pitch the story in a linear fashion. Again, you need to create a pitch that's easy listening.
Not to rain on your parade, but pitch fests yield very little in regards to success stories. Financially, it would have been more economical to buy a Powerball lottery ticket. Your odds of winning the lottery are better than scoring at a pitch fest. (Even if someone asks to read your script, it will lead nowhere.) Manage your expectations and don't go with the goal of selling your script. It's not going to happen.
Go to meet people & network. Go to share your screenplay with professionals in the hopes of being a better storyteller. Pitch fests are a waste of time & money if you don't view them as an educational experience.
Oh, and have fun. You'll enjoy the festival more if you have fun - and the people you pitch to will be more relaxed and open to your story.
Good luck!