Until what time can one put on Tefillin?

Ideally, one should wear Tefillin during the Shacharit prayer (see Shulchan Aruch, Orach Chaim, Siman 25, Seif 4). If one did not put on Tefillin during Shacharit, they can do so until sunset. If unable to put them on by sunset, they can, as a last resort, put them on until 13 and a half minutes after sunset.