I'm so sorry you're going through this. I just went through this last month. My first blood test results and the ultrasound was fine, they didn't detect anything but the 2nd blood test results were off.
On the day of my appt for Amnio they did a comprehensive ultrasound, took about 30 minutes or slightly more. The amnio wasn't bad at all. The wait time to see the doc was more than an hour but the amnio itself only took about 15 min and that's including prep time(cleaning the are etc.) It was like getting blood drawn. I had the procedure on a Friday so I took the rest of the day off, I pretty much bed rest the whole of Friday and Saturday I was up and about but didn't do anything heavy. The doc said I should just rest Friday but I just took it a step further as I was really scared of something happening. Its good if you can find someone to care for your DC while you're at the procedure. That way you can relax and focus better.
I received the results in 2 weeks or so and all was good. Good luck. Please feel free to ask me anything if you have questions.
DD1 September 2008
DD2 March 2011