This was added to the platform interface in flutter/plugins#3365, but it was never implemented (it was landed prior to the current policy of not landing platform interface changes until a combo PR is complete and fully reviewed, to prevent exactly this kind of issue).

On every platform except the legacy Android implementation, the SDK doesn't have any inherent support for this, so it would just be a timer that calls the stop method after the elapsed time, which can just as easily be done at the client level. Given that, it's not something we want to add support for in the future, so we should clearly mark it as unused. (Ideally we would remove it, but that would be a breaking change to the platform interface).