my @items = values %$rss;
my @sorted_items = sort {
    $a->{'nzgls'}{'unixtime'} <=> $b->{'nzgls'}{'unixtime'}
} @items;
# or just
# my @sorted_items = sort {
#     $a->{'nzgls'}{'unixtime'} <=> $b->{'nzgls'}{'unixtime'}
# } values %$rss;