If you want to know, I ignored everything except the potato and the plate; by going fast enough, even temperature becomes obsolete.
The first two levels are trivial and can be completed in 0.45 seconds each.
Level 3 takes a bit of effort (moving your mouse in a spiral takes a while), but I normally finish it in about a second and a half.
Level 4 I do impressively fast, since when you move off the button, the door will fully open before starting to close, allowing me to sneak through with no time loss. I finish it in about 0.8 seconds!
Now, Level 5 is interesting: the whole premise is to grab the stone so that you can cool down while moving the hot potato. Thankfully, I can ignore all of that by moving the potato fast enough, though the temperature is much closer here. I think that Level 5 takes me about 2 seconds on a good run.
Level 6 is the bane of my existence, as it regularly requires a lot of time and cooling down to complete. I found that it is possible to quickly get through the first door after pressing the button, but there seemed to be a wall blocking me about 60-70% of the time. Later, I discovered that by waiting on the button for about a second, it was much easier to get through the door and finish the level. This level alone costs me about 3 and a half seconds, along with many runs dying to the temperature.
Anyways, the last two levels are thankfully easy, with proper navigation taking 1.5 seconds on Level 7 and about 0.8 seconds on Level 8. In Level 8 it should be noted that I wait for the proper alignment and then go clockwise through the circle.
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I think a sub-9 is possible, but I'm not sure; playing on a smaller screen may help save time too.