So the films starts off establishing that they are all smart, and the sister likes to film. The whole film is done in the found footage format.
The story is actually interesting when you break it down. The whole ground hog moment, was to establish the beginning of the ripple effect. Every time Quinn entered the Chemistry room, he showed cockiness and preparations, which led the teacher to throw curve ball questions. and until Quinn knew the answers to all of the possible questions he had to keep on repeating it.
The lottery ticket. "Why didn't they go back and rewrite it" as Adam said he didn't want to waste his time worrying that some how they cheated and being in that panic mode. Remember how nervous their were filling in the paper and get away from the store after. Plus this was, plus don't forget this is still all experiments for them. They can go back and win more lotteries any time they wanted to.
David kept on pushing the machines ability to travel further by using the time watchers. Remember in the begging he said that they can only go back as far as 3 weeks, but later he said it can be possible to go back up to 10 years. Next step was 3 month: Lollapalooza. we did hear his sister say that she missed out.
This is where it starts to get more complicated and can be taken in two theories. After the failed kiss David goes back to Lollapalooza and if we see carefully he is walking at fast paced and his friends say "Oh there he is." "Looks like he is actually gonna do it" So we can assume that there was a period of time in which the first time David was away trying to get the courage to approach her, and the second David timed it so that he would take her on this walk before he managed to get there. Still don't get it? Think of Back to the future when Marty goes back for the second time and has to make sure he doesn't run into himself in the past.
David going all the way back to his 7th birthday after Jessie's disappearing. We saw Quinn nearly disappear when he started to look at himself, but the guys quickly moved him away from his sight. They broke the circle of both consciousness trying to comprehend what was happening. Unfortunately for Jessie, David didn't do that and let the circle complete erasing her at the present time line. So if he was to go back another day, she would still exist in that period. But not from Tuesday 7pm or whatever it was.
David destroying the machine in the end is paradox. No its not, and here is why in the first video of him being seen in the mirror. His father is lighting up the candles, when he goes back in the end, his father is talking to his mother. In the first Video when they figure out that the keys belong to Jessie and re watch the video, there is no blood on his hand, when he is there in the end, the blood is clearly visible. Him trying to save his father the first time, theory. His father clearly states "You figured it... i have so many questions" Obviously his father knew that he wasn't going to figure it out. and most importantly why was he hiding it after the mysterious phone call? he knew that he was going to die, probably for not handing over the machine to the government. "Why you ask?' well because David in the end says "its time for you to say goodbye to your son" and the father's line to the young version of David "A friend, he is here to fix something" My assumption on this, is that his father knew the risks with the machine, and was hoping to either have more to study it or die protecting its secret. After seeing his son, he clearly understood what he was there to do.
So why was David in the first video originally, Because the movie we were watching was not the prime time line, but rather already altered time line where David wanted to speak to his father in hopes of figuring out what can be done to try and change the future. Second time line David came back a few moments later. Remember him stopping at the door for few seconds? No? re watch it. David would not have been caught in the Party camera the second time. Through the clips when David was watching all of the party moments, The camera captured the moment when his father was talking to the mother about the call and was in a different angle, so he erased any evidence of himself at that party from that camera. He burnt all of the notes and destroyed the machine as he did that we see that he starts to flicker. That happens, because destroying the machine means you destroy the one that is in your backpack, and if the one in your back pack never existed then you never came here. The camera CAN BE (ad argued for a plot hole but) explained as just a object, which could not alter the universe (Like leaving a stick behind) Camera doesn't have any living organisms or bacteria. The end is them seeing the second camera and discovering that they learned how to time travel, and seeing presumable everything that we saw in the film. So when he walks up to Jessie at the end, he already seen it and knew what she was going to say. But they no longer can time travel, as the machine or the blue prints don't exist
Hope you guys liked my review! and any questions feel free to send me a message.