The Big Bang !
A day, without a yesterday !
Well, all that happened on the first "day", was that light separated from darkness. Somehow I doubt that process took 24 earth hours/sarc.
In fact aren't cosmologists now postulating that a microdot that contained all the known matter of our universe was expanded into something the size of a basketball in something like (10 to the neg 35th power) seconds and then continued to accelerate from there to form all galaxies, stars, planets? That was "day 2-3"