The problem is because of your unnecessary transition through datenum. When you do this:
Start= datenum(answer(1,1));
matlab interprets the ambiguous date input with the 'mm-dd-yyyy ...' (datenum) format , so, at this point your date is already stored wrong. Note that in the next line:
Starttime=datetime(Start,'ConvertFrom','datenum', 'InputFormat', 'dd-MM-yyyy hh:mm:ss');
the 'InputFormat' has no effect since a datenum doesn't have a format. A datenum can only be interpreted one way.
You could fix it by telling matlab how to convert the text to datenum:
Start = datenum(answer{1}, 'dd-mm-yyyy HH:MM:SS'); %proper to acess answer. Note that datenum format syntax differs from datetime format syntax.
But the simplest thing is to get rid of that unnecessary transition through datenum:
Starttime = datetime(answer{1}, 'InputFormat', 'dd-MM-yyyy hh:mm:ss');
Finally, note that accessing the content of cell arrays is done with {} not (), and when indexing vectors linear indexing is safer and simpler than 2D indexing. Hence, answer{1} instead of answer(1, 1).
