> Downloading from this certain website over 2 days
> now and I can't keep it running like this. Is there
> anyway I can stop at a certain point and continue
> after pc restarts?
"Continue an interrupted mirror".

But the best way is to abort smoothly (not interrupting httrack immediately or
shutting down the pc) by pressing "Cancel" and confirming "Stop", and waiting
pending transfer to finish.

You may want to check out if you did not download too much material, and if
necessary, reduce the mirror scope by addint more filters on the next session
(you may "Continue an interrupted mirror" and modify filters)