That might depend upon when you normally receive your money. My signing day is Thursday, with the money available in my account on the FOLLOWING Tuesday. Based on that, your money for 'signing' (without actually having to do so) on Wednesday 28th would be due into your account on Monday 2nd January. You MIGHT get it before Christmas but it could also go into your account on 28th, 29th or 30th December and still be regarded as 'early'.
From my own experience in previous years I suspect that you will actually get your money before Christmas - but please don't ask me to guarantee it!
Chris