... but it can't confuse other DC-clients, because filelst is (compressed) XML - unknown XML section must be ignored by other clients.
IMHO not so many times, because it will be even less of 10 bytes (seconds since 1970-01-01) per file (due to compression).
And last but not least: why we must lose any information about file(s)?
Well, saving timestamps is really good idea! ;)