I'd pot them up and give them a chance to grow a bit

Plug plants are usually too tiny to cope put straight into the ground. They're almost always better grown on in pots, unless jumbo plugs which you're going to put in a container or basket.

At the very least, they will need hardening off. Plug plants are normally grown in a close atmosphere in a greenhouse, and will need a sheltered location to get used to the wild outdoors.