I guess it would depend how far "off" your 4 patches are. Just for the essence of time, I would just square up the 16 patch block, not the 4 patch. Technically you should not have to trim or square up at all. If your 4 patches are off a significant amount, I would suggest you slow down and really examine what is causing your problem---is it inaccurate cutting or inaccurate/inconsistent seam allowances? Once you get the problem corrected you should be off and running and not have to spend a lot of time trimming.