You can use the maximum connections per second option to accomplish this.  You
may not have noticed, but that option offers some options that are less than
one per second.  As an example, .1.  If you chose this option then WinHTTrack
would read one page every 10 seconds.  You can type any value in that field
that you want.  As an example, if you wanted to read no more than one page
every three seconds, you could put a value of .33 into that field.  If you
wanted to read one page per minute then you would choose the .017 option.