We have never had a criteron about time making code. Do we need one? If we do, how do we calculate the time? If not, why not?
We already have this criterion…
…in a possibly disguised way. The problem with "write this code as quickly as possible" is that you can't verify that people didn't start writing in advance, except by starting everyone at the same time. But if you start everyone at the same time, there's then no way to improve after the first answer is posted. The solution is to have a bunch of miniature challenges, posted at arbitrary times, and have people compete to be the first to solve each individual challenge.
And of course, I just described cops-and-robbers (cops setting the challenges, robbers solving them). General challenge structures for which being the first to write the code are interesting should likely be run in that format, as it already achieves most of what you're looking for in a way that fits much better onto PPCG.