with Jack we had our infant seat in car by 35 weeks but I had been flown out 3 times and spend 5 of the previous 8 weeks in and out of hospital

this time we still haven't installed either seat, we are getting our new car the week bub is being born so no point installing then taking it out mind you we do have it in the back of car just in case, as for other car well I wont be able to drive for 6 weeks so am guessing it will get done sometime during those weeks

but yeah easy to get it in, if its yours install if its a hire one I would hold off till 37 weeks or so