It counted as a day, if it was only part of a day. So, if Christ went into the grave prior to the Sabbath, it would ha e counted as the first day, the Sabbath would have been counted as the second day, then the evening until first day morning would have counted as the third day.
Thanks, Jonty. Your explanation may be the correct one. I’m just not sure why Jesus would have specified “three nights” when He could so easily have left at “three days”. This is something I have thought about and researched, and I’ll no doubt keep on thinking about it. I appreciate your input.