Oooh How exciting!!
I had mine 3 weeks ago, and it took over an hour! I think it was about an hour and 20 minutes. We went to the hospital we will be having baby at and had our scan in their ultrasound and xray department.
While we were there they took all the measurements - legs, head, arms, chest,
checked the heart (they looked at baby's heart for ages), checked brain, stomach, kidneys and some others... they also asked us if we wanted to know the sex or not. We said we didnt want to know just yet, so they didnt look for the sex, but if we had said yes, they would have looked to see if they could tell the sex.