Thomas K. Johansen of the Centre of Hellenic Studies at the University of Bristol has written an academic paper^(a) on the degree of truth to be found within Timaeus and Critias. I don’t think it is unfair to consider his work as sceptical, even though he acknowledges the possibility of some historical foundation to be found in the text.

^(a) http://www.dur.ac.uk/Classics/histos/1998/johansen.html