"yet" goes perfectly fine with the present tense. You should have no hesitation in using that combination.
I'd definitely use the first.
On the the other hand, it doesn't seem to have anything to do with the
set-up you gave at the beginning of your post. If I were taking
up two spots and someone told me to move over, I might say, "I'm saving
a space for a friend. He's not here yet."
CJ