Translation:Shulchan Aruch/Orach Chaim/30
30: Time of Putting Them on
1 The time to put them on in the morning is from when one can see his friend, with whom he is somewhat acquainted, from four cubits away, and recognize him.
2 One is prohibited to put tefillin on at night since he may forget them and sleep in them. If he put them on before the sun sets and it gets dark, even if he they are on him the whole night, it is permitted; and we do not teach this. If he did not remove the tefillin once the sun set since there was no place to guard them and left them on to protect them, this is allowed and is such taught.
3 If one wanted to go out on the way early in the morning, he puts them on, and when their time comes, he should feel them and make the bracha since there is no need to be concerned that he may sleep in them, since he got up and went on the way.
4 If one was travelling and tefillin are on his head and the sun set, or if he was sitting in the bais midrash and tefillin are on his head and Shabbos arrived, he should place his hand on them until he reaches the house. And if there is a house close to the wall that they can be guarded there, he removes them and leaves them there.
5 There is an opinion that maintains that if one davened maariv while yet day and has not yet put on tefillin he may no longer put them on afterwards.