When using HTTRACK to mirror web sites, most file 
often don't change but HTTRACK sends an "is file 
modified" inquiry for every file. This is very time 
and bandwidth consuming. E.g. when start HTTRACK two 
times in a row, I still can take hours to discover 
that nothing has to be done.

A simple features could greatly improve this:

Only ask for "is modified" if the local file is older 
then x days (or even better has not been checked be 
httrack for x hours or days). x should be configurable 
in hours or days and a file matching mask. E.g. in an 
web archive, html files change very often linking to 
ZIP or JPG files which usually never chanve.

When I know that e.g. ZIP (almost) never change I 
could include a rule like "check *.ZIP only every 1000 
days". Then starting HTTRACK a second time would 
finish whithin a couple of seconds or minutes.