I go on Tuesday to have one done apparently it is routine if you are overdue
I have a weekly one. They monitor the babies heartbeat and movement. It is to ensure that when ur baby moves, his/her heartbeat increases. Mine take anywhere from 25 minutes to an hour. It all depends on baby cooperation. I find if I eat and have a glass of OJ a half hour before it goes faster. Good luck!
Don't worry about it! Here in Spain the do it weekly to every pregnant woman in the last couple of weeks of pregnancy to see how baby reacts to contractions. It's routinary for us. It doesn't hurt or anything, you just lay there and hear your baby's heartbeat :)
I was getting them two times a week. They didnt monitor for 4 hours though. I was usually there about an hour to an hour and a half depending on how active the baby was. He isnt a morning person so it was hard to get him moving. Lol
I have when i got in a car accident a couple months ago. All they do is put a fetal heart monitor and a contraction monitor on you and watch them for four or so hours. Nothing crazy or invasive.