He shouldn't have said "Thursday, October 31"
Batman says this in the beginning and I wish he hadn't. After going through my calendar this means that the movie is set in 2019. As far as I know none of the other Batman movies are set in a specific year. Doing so in this movie bugs me and I can't really explain why. Maybe it's because, for example, Batman 1989's year is left ambiguous and could thus be set in any year, even in the present but in an alternate universe, making it timeless. Because this one is implicitly set in 2019 I feel like it might date the movie one day.
Also, why would they set it in 2019? Production finished last year, and usually studios make a point of setting their movies in the year that they are released. You'd expect The Batman to be set in 2021 or 2022.