It seem that it doesn't work exactly this way. I downloaded 
part of website and next day I wanted to continue(of course 
i use "continue an interupted mirror"), but it started to 
download everything again (files written: 340, files 
updated: 340 (100%)). Maybe some time limit expired between 
two mirrors, but I want to force the httrack not to 
redownload any already downloaded files.