I believe it is an implementation detail regarding what, if any, time/date information is provided by a FTP server. Having said that, I would use a tool such as perl to parse something as ugly as file time/date stamps. If the server returns things in the 'ls' format, you cannot even rely on a consistant format, depending on how old the file is. And, since you are using perl anyway,
why not use a perl module just made for things like retrieving files from an FTP server, like Net::FTP?
I don't see any way around parsing each file reference in the returned directory listing. I don't think there is any standard way of limiting the the scope of listed files by time/date.