I don't remember if these were two different books or one book.

The book is about a girl and her younger sister and their mom. Their dad is gone (maybe military?) and the mom works all the time. The younger sister is very smart and somewhat weird. She wakes them up on time every morning just by picturing a clock in her head and uses it as an 'internal alarm.' When the main character tries to do that she makes everyone late.

The little sister is going to be in a talent show and her talent is reciting the headings of each page of either the encyclopedia or the dictionary. The younger sister gets stage fright and the older sister ends up getting onstage with her and reciting all of the headings with her. I feel like there is a competition portion to it and they end up doing it a second time at another talent show? One of the parents shows up to the talent show at the end of the book I believe.

I read this book in elementary or middle school so late 90s/early 2000s.