Reading variable length cell arrays into matrix

Question

I am using Octave 4.2 and using xlsread in a for loop to import data from several different RTDs. I am importing using the following code:

for i=rtdmin:rtdmax
  filnum=num2str(i);
  fid = strcat(pre, filnum, filtyp);
  j = exist(fid);
  if j == 2
    [num{i}, txt{i}, raw{i}, lim{i}] = xlsread(fid);
    time{i} = num{i}(:,2);
    temp{i} = num{i}(:,3);
  endif
endfor

The problem is none of the RTDs have the exact same number of readings (30,000 +-200), or stop and start at the exact same time, although the readings overlap. Because of the variable size of the data in each cell I cannot simply pull it out into a matrix in order to process the data. Can anyone suggest a solution of how to get the data into a matrix, or can suggest a change to the existing code so the data is read into a matrix to begin with. Thank you in advance.