December 26 will be a "business day" for any requirement of Regulation Z that involves counting business days using the "precise" definition. One example is the right of rescission. If a rescindable loan closes on Thursday, December 24, the three business days for rescission will be Saturday the 26th, Monday the 28th, and Tuesday the 29th. Funds can be advanced (after verifying no one has rescinded) on Wednesday the 30th.
It's also counted a business day for the requirement that a closing disclosure be received at least 3 business days before consummation under TRID rules.
But Saturday is never a banking day or business day for Reg CC purposes.
In general, you probably only need to post a lobby (and drive-up, if applicable) notice about the closing a couple of weeks in advance.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8