Considering that there's no function in matlab that can read this creation date, why do you care?
There is also no function that allows to change it. If it's really that important to you, you could possibly hack it by reading the file as binary before and after modification and replacing the date portion of the header. Note that reading the file as text would be too dangerous, code page conversions may corrupt the binary portion of the file.
Something like the following may work. It may also irreversibly corrupt the file:
fid = fopen('yourfile.mat', 'r'); %open as binary, read-only
oldcontent = fread(fid); %read the whole lot as bytes;
fclose(fid);
%...
%do your modifications
fid = fopen('modifiedfile.mat', 'r+'); %open as binary, for reading and writing
newcontent = fread(fid);
%It would appear that the text portion of the header ends at byte 116.
%I haven't looked if this is guaranteed by the format
%If it is not, some files will get corrupted
assert(oldcontent(117) == 0, 'Unexpected byte in old file');
assert(newcontent(117) == 0, 'Unexpected byte in new file');
oldstring = char(oldcontent(1:116)');
newstring = char(newcontent(1:116)');
olddate = regexp(oldstring, '(?<=Created on: ).{3} .{3} \d+ \d+:\d+:\d+ \d{4} ', 'match', 'once');
assert(~isempty(olddate), 'Could not find date in old file');
%Note that there may be some text after the creation date that would need shifting
extents = regexp(newstring, '(?<=Created on: )(.{3} .{3} \d+ \d+:\d+:\d+ \d{4} )(.*?)( +$)', 'tokenExtents', 'once');
assert(extents(1, 1) + numel(olddate) + diff(te(2, :)) + 1 <= 116, 'Not enough room to fit date')
newstring(extents(1, 1) : extents(1, 1) + numel(olddate) + diff(extents(2, :))) = [olddate, newstring(extents(2, 1):extents(2, 2))];
frewind(fid);
fwrite(fid, newstring);
fclose(fid);
Note that I have files with this header: MATLAB 7.3 MAT-file, Platform: PCWIN, Created on: Tue Feb 09 20:24:01 2016 HDF5 schema 1.00 ., so the code above makes sure that the text after the date is shifted appropriately.
