Yup, I ended up looking at the original data, which fortunately are also available.

That's good! Here's how I might have done it:

use warnings;
use strict;
use DateTime::Format::Strptime;

my $strp = DateTime::Format::Strptime->new(on_error=>'croak',
    pattern=>'%Y%m%dT%H:%M:%S', time_zone=>'UTC');

while (<DATA>) {
    chomp;
    my $dt;
    if ($_ eq 'today')
        { $dt = DateTime->now->truncate( to => 'day' )
            ->set( hour=>23, minute=>59, second=>59 ) }
    elsif ($_ eq 'now') { $dt = DateTime->now }
    else { $_ .= "T23:59:59" if /^\d{8}$/;
        $dt = $strp->parse_datetime($_) }
    print "$_ => ",$dt->strftime('%Y-%m-%d %H:%M:%S %Z'),"\n";
}

__DATA__
20170616T15:30:53
20170616
now
today
[download]