We put ours in a week before MJ was born and then took it out again (just so we knew that it ftted properly), i didnt see the point of driving around with it in the car... Although i was glad that we did fit it early as i needed to get an extention.
I was in hosp 6 days (emerg c/s) so it was refitted before coming to pick us up.
TBH it is the last thing that you really need to do, its not like you need it for the trip to the hopsital, so dont stress too much about it