You don’t give enough information for a specific answer.
However if you are collecting your data in a loop of some sort, save your times to a vector (or matrix, depending on how you have your study designed), then after the loop, write the vector or matrix to a file to use later. (I prefer .mat files unless you’re going to use them in applications other than MATLAB. Otherwise, save them in a file format that can be read by your other applications.)
