How do I remove the underscore a view adds to a rewritten link?
This issue happens when the field value is rendered with HTML (which is appended by Drupal date formats).
In your View, edit your time field and make sure to use Custom formatter rather than any of the predefined ones, and provide the custom pattern in 'Date/time format' field. And then underscore should go. Check this useful answer.
In my case I was struggling with underscore appended after Year value (mysirte.com/tag/1994_), and when I created custom format and used 'Y' the underscore disappeared, see picture: