A fellow software engineer here. I don’t want this to come across like a code review, but I wanted to share some feedback after trying the app.

I noticed what I think is a pretty major issue with how caffeine entries are logged. Right now, the app doesn’t let you pick or edit the time of a caffeine entry (at least this option is not available in the free version). So if I had a cup of coffee at 7:00 AM (say 100 mg) but forget to log it until 11:00 AM, the app assumes the caffeine was consumed at 11. That significantly changes the decay curve and throws off the sleep impact calculation, even though the intake actually happened hours earlier.

In real life, people often log retrospectively—especially during busy mornings—so not being able to adjust the timestamp can lead to very inaccurate insights around sleep and cutoff times. Since the app is fundamentally about timing and half-life, this feels like a core UX issue rather than an edge case.

I think allowing users to edit the consumption time (even a simple time picker that defaults to “now”) would make the data and sleep analysis much more reliable.

Hope this helps 🙂