I assume this is due to their Christmas break.
I find that to be different for AIB, where SO's for monday don't actually leave till the monday morning and the funds are still there during Saturday and Sunday.So if something is due to be credited to / debited from your account on a Monday, it will actually be accessible / gone from your account on the Saturday morning (following Friday's overnight update)
UB states said:Manage your money online 24 hours a day, 365 days a year*