Time to first response is calculated by subtracting the value of the topic’s created_at field from the value of the created_at field of the topic’s first reply. The first reply is the first post in a topic that has a post_number greater than 1 and has a post_type of 1. (a post_type of 1 is used to indicate that a post is a ‘regular’ post, and not a small action, moderator action, or whisper post.)