use Data::Dumper;
while (<DATA>) {
    @res = map { split } /(\d{4}(?:-\d\d){2}).*dates processed: (.*)/;
    warn Dumper \@res;
}

__DATA__
2009-02-02 06:12:57,500 dates processed: 2009-01-31, 2009-01-29, 2009-01-30
2009-02-18 06:03:47,713 dates processed: 2009-02-16, 2009-02-17
2009-02-19 05:58:29,138 dates processed: 2009-02-18