Not it doesn't. ->last_modified returns epoch time (as returned by time).

>perl -MLWP -E"say LWP::UserAgent->new->get('http://www.perlmonks.org'
+)->last_modified"
1253197990
[download]

You can format the result by using localtime or gmtime with POSIX's strftime. Alternatively, every date module out there accepts epoch time as an input.