This works for me:
ExcelName = 'Ekaterina Serikova error.xlsx';
% [dates,big]=xlsread(ExcelName,'Big','A2:AIF71'); % Worksheet 'Big' Does Not Exist In Your File
[dates,big]=xlsread(ExcelName,'A2:AIF71');
DN = datenum(big); % Using ‘datenum’
DN_Check = datevec(DN(1:5))
DT = datetime(big); % Using ‘datetime’
DT_Check = DT(1:5)
