Can you confirm beta 907 is using the new API? I can't find any differences in $asctime compared to no-beta, but /timeapi no longer reports any messages to indicate if it's switching the API on/off.
What makes it look like the new API isn't enabled is that the no-differences also includes reverting to the old behavior of $asctime(N) not recognizing negative numbers or $ctime(string) not recognizing dates prior to 1970.