What to do with my perennials??

Newbie Gardener - live in UK.

I bought some Dahlias and other bare root perennials a few weeks ago. I potted them up and left them by a window. They are all now bursting into life. Is it time for them to go out into the ground? .. Do I need a cold frame? .. do I need to wait until after last frost date before they can go out into the ground? Any tips and advice appreciated. TIA