The possibility to add an experiment that you started in the past, or add active days of experiments after the fact that you started it in the app. This would enable one to conceive of experiments in daily life more organically/intuitively and not always know beforehand that you are gonna start an experiment with something.

Use case example: I recently had to cancel an experiment because it somehow didn’t work to click yes on completed, only no, and so it became a frustrating that the experiment that I had started two days ago now would be useless (or less useful) because of this.