An old habit
Long before phones, people kept a line a day: one question, one short answer, the same page a year later. The habit survives because it is small.
Done badly it becomes a chore within a week. Done properly it can run for years, so it is worth getting the details right.
The question should change
The same question every night stops being a question after a few days. You answer it the way you answered yesterday, from habit, without looking.
A different question each evening makes you look again. The day has more than one side, and a rotating question visits each of them in turn.
It should follow yesterday
The best question tonight is often the one that picks up what you said last night. If yesterday your energy was low and you were somewhere else in your head, tonight should ask about sleep, or about what was occupying you.
A question that remembers feels like being asked by someone who was listening. A question that forgets feels like a form.
Ask it at the same hour
A question that arrives at a random time is easy to leave for later, and later is tomorrow. The same hour every evening turns it into part of the day rather than a task on top of it.
Late evening works for most people, close to the point where the day is finished and can be looked at whole.
If you go to bed late some nights, let the hour be yours rather than the clock's. A day that ends at one in the morning is still the same day.
Answer in ten seconds
Answer on a scale, or with a single tap among a few options, not in a sentence. The point is to look, briefly and honestly, and move on.
If an answer takes longer than ten seconds, the question was too big or the hour was wrong. Ten seconds is a feature, not a shortcut.
Do not go back and change an answer the next morning. The evening answer is the honest one, even when it looks wrong in daylight.
Where the questions come from
Insenia asks five of these each evening instead of one, generated for you each night from your profile and your past answers. A question on day two follows up on day one, and once or twice a week there is one you did not expect.
You can read the kind of questions it asks inthe question library, each with why it is asked and what it tends to show over weeks.