LinkValidationRunner.ValidateLinksOnPage times out after first link

Description

In the Admin > Link Status page, if the refresh button is clicked for a page with multiple links, only the first link is updated.

This is caused by a check for long running jobs that's called after each link validation. In ValidateLinksOnPage, the start time for the check isn't set to the current time when starting, so it always compares to DateTime.Min and times out after the first link.

The link validation scheduled job sets the start time and does not have the same issue.