I've recently watched several talks of Matt Walker [1], a sleep scientiest. And he often states that it is not only important to sleep enough, but to do it on a regular schedule. So that the body and mind can adapt. So perhaps there is a good reason why most sleep management want to enforce a fixed schedule. Nevertheless, if that is not possible, it would certainly be helpful to have such a tool you describe.

[1]: https://www.ted.com/talks/matt_walker_sleep_is_your_superpow...