@ekdodo They mostly send the interview letter (IL) on Mondays, but I've seen our friends report getting ILs on Wednesday (@intelcorei5) and Friday too (@MYusuf, @mertdzkr, and @cokbekledik86). This makes sense because they do the interviews on Tuesday and Thursday, so the other days are open for desk work (e.g., scheduling).
Recently, they've consistently sent the ILs about 45-50 days before the actual interview (@cokbekledik86 is an outlier with a 62-day notice). The first interview dates for February are the 2nd and 7th. Forty-five days days before the 2nd is today (December 19th); 45-days before the 7th is December 24th. So I expect IL emails this week on either Wednesday or Friday or the same days next week (Monday the 26th is a holiday).