For resizing/extracting the data with respect to the dates given in a different table, joining tables would be helpful. You can also use indexing techniques to extract a part of the table as shown:
% Extract two middle rows of a 2*3*4 matrix
a = reshape(1:24, [2 3 4]);
a(:,:,2:3)
Since you have just mentioned that you need to replace the time in your data, I am assuming that you want to parse the dates in your data which can then be converted to a number of representations. The parsing of dates can be done using the DateStrings argument of the datetime function.
