1) This project won't take so much time.
2) This project won't take that much time.
Is there any difference between the meanings of these sentences?
I am not a teacher.
They could both be used if the project is being compared to a length of time previously mentioned, and in that sense they would have the same meaning. I would use 'as' instead of 'so', though.
I wouldn't use 1) as a stand-alone sentence.
I would use 2) with stress on the word 'that' to mean, 'This project won't take much time, or at least not as much as you might think.'