I had a gorgeous Acer in a 'waisted' pot and had the same issue. It was getting too large for the pot and I decided to plant it out into the garden. Since it is in the pot, you could probably plant at any time of the year. Now should be fine and over winter it will not dry out.

You may, however, find it difficult to get them out of their pots if they are now quite large. Especially if they are 'waisted' pots. And beware, they may have been constrained in the pots and when planted in the garden, they could grow to be rather large trees. If you know the varieties, check their potential size before choosing where to plant them.

as they in pots they can go out when ever you like. it is just like buying a plant from the gc and planting it when convenient.
If the roots are congested tease them out a bit. A bigger hole than the pot as I am sure you know.

I hope you are successful Lincs in transferring the Acers..
I can remember doing that with one of ours...we did water the Acer thoroughly well before....the pot was a casualty but the tree survived!

Somhairie, Seaburn and Meadowland....Thankyou all for responding, I wasn't sure whether it would be too late this year but knew the best people to ask, I'll have to decide where to place them, I'll keep you posted ....xx