Thanks, Xavier. I think I found a solution.

I found the refresh.html file that the httrack server sends
to the browser in the /usr/local/doc/httrack/html directory.
In the Javascript code I found two occurences of the value
500 (if I remember correctly), which seemed to have to do
with the reloading functions. So I changed them both to
10000 (10 seconds) and saved the file back (as root). It
seems to work nicely. The page now only reloads every 10
seconds.