Yes as Mitch says it’s 3 months. If you log into your motabillity account it will tell you the exact date you can order and the date you hand your current car back, which is exactly 3 years to get day that you picked your current car up.
In my case I can order on the 16th Feb but can’t hand car back until 17th of may at the earliest. So if I found a stock car on the 16th of February it would be no use as I can’t hand my current car back until the 17th of may. Unless a dealer is willing to hold it over for you for three months. Mind id imagine that if it had plenty of expensive optional extras they might hold it.