In a practical sense, there just cannot be aliens zipping around in “normal space” in any sense of the word.
Just to get to the nearest star to our sun, Proxima Centauri, is 4.2 light years away. To get there in three weeks, someone would need to travel at 64 times the speed of light. The closest star that comes even theoretically close to maybe having a habitable planet is Gliese 581g, at over 20 light years away.
This means that space aliens would almost have to travel via an “alternative space”, where relative distances are much less.
The other night as I was waiting for sleep I tried to imagine the immensity of space. I imagined flying past uncountable galaxies as far as you could see.
Then I thought, try to imagine not the scale of galaxies but at the scale of me. For a fraction of an instant I succeeded.
It about precipitated a panic attack. It felt like an elephant was sitting on my chest and I a hundred feelings I can’t express went thought me.
I quickly went back to the galaxy scaled imagining. The raw reality of the size of the universe is too much for our limited psyches to accept.
That's three weeks our time. It could be done in three weeks of subjective time, i.e. three weeks of time as measured from the spacecraft, at a much lower rate of speed... some large percentage of C. I've forgotten how to run the Lorentz equations to figure it exactly, but it can be done.