Punctual, Millenium trilogy, Lisbeth Salander/Miriam Wu
When Lisbeth comes home to Miriam, Miriam is upset, and Lisbeth has no idea why. She was supposed to show up today, the fifth, at around seven, wasn't she? And they never promised each other to be faithful, it's not their thing. She tries to tell Miriam this, and Miriam throws a pillow at her and yells.
"It was last month you were supposed to come home!"