Hack the review submission timestamp.

The createdOn timestamp on the patch isn't what we want.
It's when the patch was written, not submitted for review.
The next best thing in the data we have is the time of the
first review.  When all is working well, jenkins or smokestack
will comment within the first hour or two, so that's better
than the other timestamp, which may reflect that the code
was written many weeks ago, even though it was just recently
submitted for review.