Awesome time travel game mechanic :)
I'd even say its better than the submissions of the theme 'Inversion' I saw back then, where some jammers have choosen a similar way.
The graphics are elegantly simple but still fitting well to the theme.
Keep jamming :)
PS: +1 for volume controls. I always add this accessibility feature since some submissions blast my ears off ^^*
I have one suggestion: Your volume slider seem to control the sound linearly, but dB is a logarithmic unit. So only the last 10-20% of your slider are usable since the sound is just quiet at the remaining part. Use something like linear2db to convert the volume position to decibel.