a) You must be trying to use parfor on the outer i loop, but this does not allow you to make an assignment to the jth page of January as parfor will not allow this.
b) Why do you need a loop? (See vectorized example)
c) Why do you need to do this in parallel? (This is not a large problem, but if you want just move the parfor to the inside loop)
Try to use vectorization:
% Create a matrix to represent your data:
S = (1:744*6)';
S = reshape(S,744,6); % S now has the format you mentioned
% Now we can just do a reshape on the transposed data and then permute:
S2 = reshape(S.',6,24,[]);
S3 = permute(S2,[2 1 3]);
