Based on the words of the MC, it should be Monday on the last pages of the chapter. Then this new fellow shows up and text him on Monday morning, wondering if he's at home. And since he doesn't get a reply, decides to just pop by. Why? The most standard thing in that situation would be thinking he's at work, and contact him around noon or in the evening again, not go to his place thinking that he's at home and just not replying to you. Also, apparently he didn't even give him any time to reply, but just instantly jumps to conclusions. I already dislike this new guy, even though we know pretty much nothing about him.