In that case it is no really a time, it is a condition.

If the “condition” is what’s important for whatever you want to achieve, then that’s the thing to store.

Moreover, most people in real life will understand that to be a time and won’t care how it maps to UTC.

Yup, it's a function that leads to a time, depending on some things. And you can't express it in UTC, so you better store the whole function (as a string, for example). QED