What you are seeing is flow — the state where your child feels their best and is fully engaged. Your tween is absorbed in a book and the required work is waiting. This is the age where the internal scaffold starts to matter more than the external one. A tween who can manage their own reading time alongside their responsibilities is building genuine self-regulation. Your job is shifting from manager to consultant. The goal is not to get them to stop reading right now. It is to help them develop their own system for honoring both. If this is new language for your tween, start by modeling it yourself. The arc from parent-managed to self-managed begins with the first conversation.
I am not going to pull you out of your book. When is a good stopping point for you, and what do you need to get the work done after?