I think midnight tonight!
A general rule I have for myself when completing applications is to assume the earlier deadline, for example, Addleshaw Goddard's is 5th Jan 2020, but I would always assume it's midnight 4th Jan 2020. I think it's best to send an application earlier to avoid disappointment especially if you've spent all your time writing it to have missed the deadline by hours.
I have just checked their Instagram and I think it is tomorrow, 5th January 11.59 pm