I personally think it is probably just an idiom of speech that people of that time recognized as meaning 'parts of three days', as other Hebrew scriptures often use a phrase of "three days' but dpn't require meaning 72 hours. And after all, none of the other gospel writers or the apostle Paul ever mentioned the specifics of the time periods other than referring to the time as just "three days". Nor does it appear anyone from that time period balking over the language's possible technical meaning.
Nevertheless, there is a way to explain it so that there are 3 actual nights being involved. But you have to drop an assumption being made.
re: 3. Of those, there are some who believe that the "heart of the earth" is referring to the tomb or at the earliest to the moment when His spirit left His body.
If the "heart of the earth" doesn't refer to only his being dead in the tomb, but also
includes the time period where he was restrained, under arrest, and in custody by the authorities, then that would include the events of Thursday night/Friday morning during the night period after the celebration of the Passover he had with this disciples.
Here is a good explanation of it -
https://www.youtube.com/watch?v=-sWKdrngmCY