I finally came up with the solution, thanks to being sleep-deprived, which provided a much-needed sense of clarity. Aww, you know that!
In the feed.php, I have defined a new default:
'timefield' => 'time',
This ensures that a separate field for the time within a blog post can be processed properly.
Now, looking at the template.php, line 8 does not need to be rewritten. It apparently generates the information when the feed itself was refreshed.
Line 20, however, is key. It fetches the information from the date field of the blog post and displays it in accordance to RFC 2822 (example: Thu, 21 Dec 2000 16:01:07 +0200). All I had to do is rebuild this structure piece by piece. This allows me to jump to another echo (if that makes sense), from date to time:
<pubDate><?php echo $datefield == 'modified' ? $item->modified('D, d M Y') : $item->date('D, d M Y', $datefield) ?> <?php echo $timefield == 'modified' ? $item->modified('H:i:s O') : $item->time('H:i:s O', $timefield) ?></pubDate>
This, in fact, works wonderfully. Wow.