Same for me, you can order anytime after you have 3 months left on your lease. But you cannot collect it till your actual exchange date, mine was the 15th of april so the dealer could place an order on the 15th of jan.
No factory slot, before april was available. so he sourced 1 of 3 available from stock that was and the car was at the dealers well before lockdown. Picked it up a few weeks ago.
I think also they can add a provisional order to the system if say a certain model or trim level will not be available soon as they stopping it and it’s one you really want.. I test drove my latest car back in sept and just before xmas visited Vw for some new wipers and had alook while i was there No golfs at all… he said so anyhow he added a tig sel as the honda dealer asked me if i had ordered one as was on the system. I did look but we did not agree on anything. but I do know the sale person and he did the same with the golf i did have at the time to get the right ccolour etc i wanted as they was making the 7.5 and was only stock left.
i think was the same with the tig so he placed it, just to secure the correct car incase i decided i did want it..
Also at honda they told be the highest spec on scheme was being stopped in the uk so in jan will no longer be on the scheme and if i did want one he could sort it with mb somehow like i said but i wanted the my20 new refreshed model that was already out in the usa..