I tried slow motion with Physics - it really doesn't work very well, as setting the velocity to be demultiplied repeatedly reduces it until it hits 0 (or so close to it that there's no difference) and even if you were to figure out a way to get its proper velocity past the slowed effect, it's kind of hard to make it react as if it were moving at full speed.
A proper timescale addition to Construct would definitely be useful, as I don't believe that it can be achieved via events. At least not with Physics, which is really the only thing I'm using.
It would be nice if the timescale was added to various behaviours, but at least a global application variable would be nice and perhaps an option to apply it to an individual object at runtime.
Stopping time, on the other hand, is something I've already figured out how to do with physics.