I tried on both my Android phone and my PC in Chrome, and it worked just like on my Rokus.
I will say that the white dot on Android is huge compared to the recording line, so users need to understand that the center of the dot is what determines where the recording is. When I was trying my first recording, I put the dot right before the yellow marks, and it was still about 3 minutes away from the actual commercial. When I do it in Chrome, it is about 20 seconds before a commercial, since the line is more to scale.
I doubt this can be changed, because the user needs the dot big enough to move with their finger. Just be aware of how it works.