Mine went in the ground around then too iirc, plus a few look to have popped up as self seeded from some I had left & let flower - I moved these last week to fill gaps in the current Leek bed. They're pretty hardy.
If you mean transplanting the leek 'seedlings ' (as in those from normally seed sown in early Spring) - yeah they are hardy but they aren't going to do much growing over the winter months are they ?
You planted leeks in October ?