You should try preprocessing your table data before reading it completely. readdata() function automatically detects the datatype of the column.
As a workaround, try to read the first column of your data as text using ‘textscan’ function (https://www.mathworks.com/help/matlab/ref/textscan.html) as text and change it to one common datetime format and then read this modified data completely using readtable() function. You can, however, read the complete data using ‘textscan’ function itself and use it.
