Hi LizzieB,
Put them all in the ground - give them a chance- you can always pull some out if there are too many.
For me the most important is not the age but the length. 20 cm / 3-4 inches and most of the stem underground for it to keep its moisture. Else they desiccate too fast and can't root.
Another point is they should get sun to get warmth - if they are in a cold and shadowy spot, they are going to have a bad time rooting and growing properly.
At this point of the year, all wood on your ground is at least half hardened and this is enough to get it to root. Get ready to leave in a forest :) .
I would put them 4 by 4 at 50 cm of distance for easiness of moving them around later .
I would try some in pots for having a definitive place later - did I mention my Dalmatie cuttings in pots - 3 pots already and I already saw some root shoots that will go in pots as well for exchanging or winter backups or just
for testing the pot culture.