I would be happy to test this. It appears to block the launcher but because on the mac it loads in a Java JVM it doesn't matter that the launcher is blocked.
As discussed in many of the apple forums because apple allows the "One more minute" option a kid can bypass the launcher restriction by asking for one more minute on the launcher giving the game enough time to load and then having no limit.
This doesn't appear to be a priority issue for MoJang, but as a parent this is a big issue. I am going to have to delete this game off of my sons computer if this isn't fixed.
I am wiling and able to help test this!