First of all, this question is not about the influence of the critics in the media, it is about when (statistically) the good movies are released. While everyone has different types of tastes, "good" here refers to the rather generalized opinion about a movie, which often can be categorized quite easily into positive or negative.
Usually films are not just released when they're done but there is planning and market strategy that takes place (for example Disney releases their big movies on Thanksgiving weekend, and has historically "owned Thanksgiving"). So I think assessing the generally worst month for movies might be an interesting analysis of movie release trend history.
So what month (United States calendar) has more bad movies released in the same month?
For example I went to Rotten Tomatoes today (just an example, the question is not necessarily centered around RT critics alone) and I found this:
The 70% of the movies listed are considered bad movies (by Rotten Tomatoes). So this would seem like bad month to watch movies.