The format is not an issue but there are several ways to import. Here is one:
opts = detectImportOptions('data.txt');
opts = setvartype(opts, 'char');
tbl = readtable('data.txt',opts);
C=strcat(tbl.Date, {' '}, tbl.Time)
datetime(C,'inputformat','yyyyMMdd HHmmSS')
You can also experiment a bit more with the detectImportOptions to avoid post-processing
opts = detectImportOptions('data.txt');
opts = setvartype(opts,'Date','datetime');
opts = setvartype(opts,'Time','datetime');
opts = setvaropts(opts,'Date','InputFormat','yyyyMMdd')
opts = setvaropts(opts,'Time','InputFormat','HHmmss')
T = readtable('data.txt',opts)
