This is a reaction review for those who saw it, spoilers ahead.
This was actually a really good movie, one whose writer(s) really sat and thought through the ideas and made sense of tough conundrums without making the audience lose interest or suspension of disbelief. It had me thinking about the movie while I was in bed trying to sleep, imagining things. There were no significant plotholes that I could see, except only some science holes like why a gajillian bears, insects, and other creatures weren't piling up at the entrances, or how this time dilation--for which no origin explanation was so much as hinted nor asked about--was spinning around with the spinning and revolution of the Earth without ripping Earth to shreds. I suppose one could nitpick other minor plotholes like why wasn't there a follow-up for the future-human? Or who was in the nested double time dilation and how did they get there in this North American locality with 8th century garb. But it was just a visual effects still image, not really part of the plot, can't try to make too much sense of it. It was meant to paint a picture depicting that "humanity has been fighting over the fountain of youth for millennia".
I also wanted to react to some questions other reviewers had. 1) The girl who went up and looked around and came back down DID age with acceleration, you weren't paying attention. She wasn't gone for thirty minutes. She aged thirty minutes of her own life while onlookers didn't realize she even left (zero seconds). 2) There wasn't racism in this movie, you woke, brainless dimwits, because there were no other races. Neanderthals are not "another race" that the writers misunderstand. Neanderthals in evolutionist theory are early DNA, origins of our race, and, yes, uncivilized and animal-like in behavior because they were, literally, unevolved and civilly undeveloped. 3) There is absolutely no suggestion nor inference that the super-future evolved beings that pulled out the 21st century humans didn't, or won't, also pull out the Neanderthals and just keep them separated, or for that matter spend a few millennia trying to get at that fountain of youth. We didn't see them pulling the others out after the first few, we just saw them fully recovered afterwards, so we know that more went on. So relax, no one was left out.