mklinks is a little program I have written to manipulate directories. I'll link to it some time. It's a very powerful program, but it contains a maze of twisty little options, all different, and sometimes I find I've messed things up long after it happened. I'm writing down typical incantations here.

Replace dst with links to src where the files have same timestamp and size.

Remove all files in dst with corresponding files with same timestamp and size in src.