This is an issue, not just for breast ultrasound, but all ultrasound. The shorter the appointment time the less detailed the scan becomes. It is a simple principle.
The time I require to perform a breast ultrasound depends on the type of breast ultrasound I am performing. I can perform a targeted ultrasound to an area of palpable lump for example in 5 – 10 minutes comfortably. If I am performing a bilateral “around the clock” examination on a Birads C breast I would prefer 20 minutes. Some examinations simply take longer than others depending on the complexity of the scan and you cannot predict complexity until you begin the examination. We just rely on things averaging out with some being quick to free up time for others that are complex. This is not a new principle, I feel like it is exactly the same for obstetric examinations (nuchals and morphs especially)