Some of the heroic challenges have a 25turn award. It’s very very easy to lose track of what turn you’re at and finish the battle too early. Surely adding a discrete turn counter to the battlefield wouldn’t be too hard?
You can always check your progress on that (and all other objectives) on the pause menu on the bottom of the screen.
If you click on the small circle at the bottom of the screen (while in a duel), a list comes up that tells you your match goals and how close you are to completing them. This includes a turn count if that is one of your current goals.
Thanks! Don’t know why I haven’t found that before.