If it's still in text form (string or cellstr), it's no problem
dt=split(tTable.DateString); % split the component pieces
tTable.Date=dt(:,1); % add Date column
tTable.Time=dt(:,2); % add Time column
Both are still whatever string type started out with.
Then it's trickier and splitting may not be the best idea after all -- in MATLAB datetime class, a date can exist with a presumed time of midnight but a time cannot exist without a corresponding date; there is no such thing as a standalone absolute time in this implementation.
You either turn time into a duration of some ilk or keep the date and simply change the display format to display the time portion alone.
A better and more complete answer could depend upon what the intent of the above is to accomplish -- it may not be necessary (probably isn't) to create the two variables anyway to perform whatever tasks are intended.
Another alternative could be to use a timetable instead where the date/time is inherent in the row structure and there are some specialized tools for common tasks that may well solve the problem.
