The import process was running on the async load thread, but then
accessed from the access thread later on. This seemed to somehow pass
fine in headless runs, but would fail on visual test execution
(specifically on `TestBeatmapConfirmed()`).
- Using realtime (`DateTimeOffset.Now`) meant that values would be
changing in the same frame, causing misfirings or incorrect displays
- No debounce on sample playback meant that scheduling edge cases could
potentially cause samples to be played more than once.