I did it on 6 feb (20 weeks), it took around 20 mins. The doctor will also bring along 2 students to teach them each organs of the baby. Lucky that mine one are 2 female, the one before me are 1 male and 1 female. You have to ask questions yourself otherwise the doctor will only talk to the students throughout the structural u/s check up. The only question she proactively ask me is "do you want to know is the sex of baby?". Then, she will finally give a conclusion that whether the baby is healthy. If is healthy, no more ultrasound will be provided for the rest of the check up.