Lately I've been liking the expression, "Sometimes it's easier to ask for forgiveness than it is to ask for permission".
In my case it's not a matter of doing something without asking, but rather not doing what has been instructed.
Past experience just won't allow me to schedule testing with a third party when my client still needs to verify their approach has been approved. Admittedly it's nothing as critical as aircraft landing (that was a previous project), but it still has potential to waste time and money.
Of course I will never see that money as it was never mine, and I will inevitably be criticised for the communication delay.
Explaining will take longer than apologising, but I'm not the kind of person to apologise for doing what I feel was right.