A resposta direta à sua pergunta é que Não segue não ocorre em nenhum momento específico.
Em entrevista ao The AV Club , o escritor / diretor David Robert Mitchell discute a origem da história sendo um pesadelo recorrente desde a infância:
I’d had this idea for a long time. It came from a nightmare that I had as a kid—this basic idea of being followed by something that can look like different people and only I could see it. It was very slow and always coming for me.
Por causa disso, ele queria manter o cronograma ambíguo, ao mesmo tempo em que fazia os eventos parecerem um pouco sonhadores. Quando perguntado pelo The AV Club sobre o período de tempo e "shell-phone" mostrado no filme, Mitchell tinha isto a dizer:
There are production design elements from the ’50s on up to modern day. A lot of it is from the ’70s and ’80s. That e-reader cell phone—or “shell phone”—you’re talking about is not a real device. It’s a ’60s shell compact that we turned into a cell phone e-reader. So I wanted modern things, but if you show a specific smartphone now, it dates it. It’s too real for the movie. It would bother me anyway. So we made one up. And all of that is really just to create the effect of a dream—to place it outside of time, and to make people wonder about where they are. Those are things that I think happen to us when we have a dream.