'Don't Blink' is ambitious but ultimately falls short of its own intent.
Not all horrors or thrillers need to conform to genre tropes, and the film should be commended for it's attempt to tell a more meaningful, character driven story. Indeed, the characters are the driving force here, as an ensemble the cast perform well together, very believable and naturalistic, without anyone falling into exaggerated horror stereotypes.
This however is a double edged sword, as the cast gets 'picked off' and emotions become heightened, the performances lose that grounded and relatable quality, and out come the clichés, right down to the stark religious fanaticism and tough guy bravado.
Most reviews find a sticking point in the ending (or lack thereof) and while I did give some praise above for the attempt, I once 'attempted' a front flip whilst drunk at a cookout, but when I got to the ER, I wasn't treated for 'attempting to be cool', I was treated for a broken leg.
My point being, the attempt doesn't count for much if you can't stick the landing, and when the central narrative thrust of your movie has been uncovering the mystery of what is happening to our protagonists, you cannot then reach the end of your run-time and say 'it didn't matter, that was the point all along' and expect to have accolades thrown at your feet. The film made it matter, it doesn't get points for flipping the script in the most predictable manner in the last minute.
If the theme of the film is the fleeting impermanence of man in the face of the ceaseless march of time, therefore rendering any specific definition or conclusion meaningless, then why did you place so much significance on any meaning at all?
I am always wary of the narrative concept of the 'mystery box', as often the most satisfying part of a good mystery is seeing all the pieces come together, even if you couldn't put them all together yourself.
Now while some questions don't have answers, those questions are often existential, and are hard to convey in a satisfying manner. This film poses the question 'did any of it matter?' When the answer is a resounding 'no', then it's understandable that your audience might come away feeling that perhaps their time was wasted.
In closing, the 'mystery box' presented to the audience by 'Don't Blink' is empty. It's a pretty box, but empty all the same.