If he's not important to the story, then it doesn't matter where you introduce him; in fact, if he has literally no part in the story whatsoever just say he's died or something before the novel, so you don't have to deal with building up characteristics of a really minor character. Then again, if he plays an important role in your novel, then I would say put him at chapter twelve, maybe have him do small talk with your MC right at the beginning before exiting and returning back to the story later on. Also Day 3 on chapter 12? Either there must be a lot of things happening in your MC's life or you've over-fleshed the story. However, if you can make it work like the Percy Jackson series where the story took place for a duration of a few days, then ok, go on ahead. Chapter 12 is not that late to introduce the MC's dad...
Hope this helps.