Weekday rush hours are the main thing to plan around for Stansted to Cambridge, since the M11 and M25 get busy with commuters as well as airport traffic. An early-morning or early-evening weekday trip is worth a little extra buffer; things generally ease off in the evenings, at weekends and during school holidays. The fare stays fixed regardless of which of these you land in.
Your pickup point is confirmed ahead of time, removing any guesswork on the day, and flight tracking on airport journeys means the car adjusts to when you actually land rather than when the schedule says you should. The usual airport steps still apply either side of your drive — check-in and security, or passport control and baggage reclaim — and the included waiting time is there to cover them.
A quick note on group size and luggage at booking saves any surprise on the day: a saloon is comfortable for four with two large cases, and an estate, MPV or 8-seater takes the extra bags, buggies or kit that a bigger trip brings. Since school holidays and summer tend to be busier for journeys like this, booking a little ahead makes securing the right vehicle straightforward.