This is a question I get asked a lot at workshops and talks, and it’s an important one! Good timing choices are essential for creating a good experience.
Often times I hear designers and developers say they have one specific small number, like 200ms, to use as the duration for any and all interface animations no matter what. This sounds like a good solution, but it over-simplifies the complexities of timing and won’t always get you the best results.
Good animation timing is more of an art than a science. Thinking in terms of a range instead of one set duration value will serve you much better in your design work.