Looks really good! SFX work well, too.
I think the premise is really clever, and fits well with the count down theme.
My main concern is that the game gets very fiddly. I think there may be an issue with the inputs: because mouse click is used both to position the parts and to use the selected tool, I often had a lot of trouble getting the game to register the tool use. I wonder whether changing the control scheme might work better: for example, use E to use the selected tool.