The dealer can accept your order if they choose to, Motability however will not accept the order until the 3 month window opens.
The AP is not guaranteed until Motability have processed your order.
There’s an element of trust between you and your dealer required but it can be done and may save you a couple of months of delay.
The subject of ordering earlier has been broached many times with Motability and they remain steadfast in sticking to the 3 month rule.
If I seem a little strange, that's because I am.
Skoda Karoq SEL.