For info, even in a completely "nominal" launch there are holds. This is particularly true when you have a tight launch window. The idea is to build some slack into the countdown to allow for the possibility if correcting any unforeseen problems. This is possible because at certain points in the countdown you can safely wait for fairly long durations. So the countdown is started early with respect to its launch window, and if any minor problems crop up they can be corrected during the planned pauses without slipping the launch time, and hence missing the launch window.