When you want to enter a duration less than a day, it will generally be better understood in HH:mm:ss format by the user. Using <input type="time" /> works well in a language that's on a 24H basis, but when trying it with a browser in english :

• They have to enter AM/PM, which doesn't make sense in this context.
• They cannot enter durations over 12:59.
• Other use case : military time uses 24H cycles.

An easy workaround would be to have a way to override user's default to force 24H cycle. I think otherwise behavior is just the same as time. I'm not sure which of type="duration" or cycle="24h" would be best here.