Obviously not now any time until early March would work. You want to get the hedging in before the sap starts rising and when the ground not frozen. It doesn't matter if it freezes after you have planted.

as long as the garden isnt frozen any time before spring. as mg says before march is out.

Look for bare-rooted 'saplings' if your friend wants a hedge - they're much cheaper. That isn't the right word - I can't think of it. Anyway, they establish fast!

Thanks everybody for your answers will , pass on to my friend