I am creating a mobile app for a Shopping mall. I have animated the tab bar icons that change from line-art style to filled icon when selected. A standard UX law states that the interaction should be max 400ms. Is it right to increase the animation time to 1sec or 1.5sec.
You're referring to the Doherty Threshold. The "rule" about <400ms that came from the Doherty & Thadani research paper was around productivity. So if your app is very task-based and about facilitating user productivity as much as possible, then good to stick to <400ms. But if your app is more exploratory and content-based, probably fine to increase animation time if you feel you have a reason for it.