Gemara

(Beraisa): One blesses on Tefilin from the time to wear them. If one had to start traveling early, and for the safety of the Tefilin he must wear them, he wears them. When the proper time comes, he touches them and blesses.

Question: Until when is it permitted to wear Tefilin?

Answer #1: It is permitted until sundown.

Answer #2 (R. Yakov): It is permitted until people cease to walk outside.

Answer #3 (Chachamim): It is permitted until the time that people normally go to sleep.

Chachamim and R. Yakov agree (with the first Tana) that if one removed his Tefilin, he may not put it on again after sundown

Some say that Rav Nachman ruled like R. Yakov. Some say that he ruled unlike R. Yakov.

Rav Chisda and Rabah bar Rav Huna wore Tefilin during prayer at night.

Question: Rabah bar Rav Huna taught that when it is Safek night, one need not remove Tefilin, nor may one put them on. This implies that when it is Vadai night, one must remove Tefilin!

Answer: Rabah's teaching refers to Erev Shabbos.

Question: If he holds that the Mitzvah applies at night, he should hold that it applies also on Shabbos, for the same source to exclude Shabbos excludes night!

Beraisa - R. Yosi ha'Galili): (After the Mitzvah of Tefilin it says) "v'Shamarta Es ha'Chukah ha'Zos l'Mo'adah mi'Yamim Yamimah." 'Yamim' excludes nights. "Mi'Yamim" excludes some days, i.e. Shabbos and Yom Tov.

R. Akiva says, the 'Chok' referred to is Pesach (which was discussed before Tefilin).

Answer: Rabah holds like R. Akiva, who learns from "v'Hayah l'Os Al Yadcha..." - the Mitzvah applies only on days when Yisrael need an Os (sign that they are Hash-m's nation), but not Shabbos or Yom Tov, which are themselves Osos.

(R. Elazar): One who wears Tefilin at night transgresses an Aseh;

(R. Yochanan): He transgresses a Lav.

(R. Elazar): One may wear Tefilin at night in order to guard them.

Ravina: I saw Rav Ashi put on Tefilin at night. I asked if this was in order to guard them, and he said 'yes'. I could tell that it really wasn't in order to guard them. He holds that the Halachah permits this, but Ein Morin Ken (we do not tell this to one who asks).

Berachos 9b (Mishnah - Acherim): The time to say the morning Shma begins when one can recognize a friend four Amos away.

(Abaye): The Halachah follows Acherim regarding the time for Tefilin

Eruvin 96a (Beraisa - R. Noson): One awake at night may remove or put on Tefilin;

Yonason ha'Kitoni says, one may not put on Tefilin at night.

Rishonim

Rif and Rosh (Hilchos Tefilin 9a and 16): One may wear Tefilin at night, but Ein Morin Ken.

Rif (ibid.): The Halachah follows Acherim regarding the time for Tefilin.

R. Yonah (DH Amar): Some texts say 'the Halachah follows Acherim regarding the time for Tefilah. Other texts say 'for Tefilin', but surely Laylah Zman Tefilin. However, Chachamim were concerned because people sleep then, and perhaps one will pass gas in them. Chachamim said that the Halachah permits, but Ein Morin Ken. Abaye holds that one may wear Tefilin before when one can recognize a friend, but if one asks, we tell him this time.

Rambam (Hilchos Tefilin 4:10): The time to wear Tefilin is during the day, and not at night, for it says "mi'Yamim Yamimah." "Chukah" refers to Tefilin. The time for Tefilin is from when one can recognize a friend four Amos away, until sundown.

Rambam (11): If one put on Tefilin before Shki'ah (sundown) and it became dark, even if they are on the entire night, it is permitted, but Ein Morin Ken.

Rosh (17): The Rif's text says that Rav Ashi did not remove his Tefilin at night. All our texts, including Rashi's, say that he put on Tefilin at night. Sefer ha'Terumah says that we hold that Laylah Zman Tefilin, i.e. one need not remove Tefilin immediately at night, but l'Chatchilah one may not put them on at night. Chachamim and R. Yakov hold that Laylah Zman Tefilin, but they agree that if one removed them, he may not put them on again after Shki'ah. If they held that Laylah Lav Zman Tefilin, surely they would not permit wearing them until the market is empty or until going to sleep. Since the Torah forbids putting them on, it forbids also leaving them on. "Hishamer" is an Aseh that obligates removing them. This is why in Eretz Yisrael they blessed when removing them close to Shki'ah. The verse commands to guard the Chok to wear them only during the day, but not at night. Rabah bar Rav Huna wore Tefilin at night. We asked that he said that one need not remove Tefilin when it is Safek night, which implies that one must remove them at Vadai night. We answered that this refers to Erev Shabbos. During the week one need not remove Tefilin at night, for Laylah Zman Tefilin. On Shabbos, when one may not put on Tefilin, one must remove Tefilin at Shki'ah. The opinion that Laylah Lav Zman Tefilin similarly obligates removing Tefilin immediately at dark. The opinion that Laylah Zman Tefilin does not obligate removing Tefilin at night, but one may not put on Tefilin then, lest he sleep with them on. In Eruvin we say that at night, one may remove or be Meni'ach Tefilin. Meni'ach means to leave them on. If it meant to put them on, we would not need to say that he need not remove them! Rather, he may remove or be Meni'ach, i.e. refrain from removing them. Ba'al ha'Itur says differently in the name of Ge'onim; what I wrote is primary.

Poskim

Shulchan Aruch (OC 30:1): The time to put on Tefilin in the morning is when one can recognize an acquaintance with whom he is slightly familiar, four Amos away.

Mishnah Berurah (1): Until this time, we are concerned lest he sleep in them. Regarding Tefilin, until this time is considered night.

Shulchan Aruch (2): One may not put on Tefilin at night, lest he forget them and sleep in them. If he put them on before Shki'ah and it became dark, even if they are on the entire night, it is permitted, but Ein Morin Ken.

Beis Yosef (OC 30 DH u'Mah she'Chosav Rabeinu Hainu): The Rambam rules like the opinion that Laylah Lav Zman Tefilin, and one who puts them on them transgresses a Lav. Even so, if he put them before Shki'ah and it became dark, even if they are on the entire night, it is permitted, but Ein Morin Ken. He learns from Rav Ashi. Even though he holds that Laylah Lav Zman Tefilin, he did not remove them. I.e. the Isur is only to put them on at night, but one may keep them, but Ein Morin Ken.

Magen Avraham (2): The Beis Yosef says here that 'Shki'ah' here means Tzeis ha'Kochavim. In Siman 25, he brought from Hagahos Maimoniyos that one removes Tefilin in Keri'as Shma of Ma'ariv. This refers to one who prays Ma'ariv during the day.

Magen Avraham (3): Since Ein Morin Ken, in public one must remove them.

Gra (DH Asur): We hold that Laylah Zman Tefilin, for the Halachah follows R. Akiva against his colleague. R. Yakov and Chachamim agree. Rav Chisda and Rabah bar Rav Huna rule like this, and Rav Nachman according to one version, and also Rav Ashi. This is unlike the Rambam, who rules that Laylah Lav Zman Tefilin, like R. Elazar and R. Yochanan, and he explains that Rav Ashi forbids only putting them on at night. The Yerushalmi is like this. All the Poskim say that Rav Ashi holds that Laylah Zman Tefilin, but even so one may not put them on then.

Mishnah Berurah (3): The Magen Avraham connotes that one may put them on Bein ha'Shemashos. The Pri Megadim was unsure, unless he did not yet fulfill Tefilin today.

Mishnah Berurah (7): At night, one must remove them even to sleep Arai (a short nap). Perhaps this is according to letter of the law.

Sha'arei Teshuvah (2/3): I wrote above (18:3) that the Ari Zal was very careful to remove Tefilin after Shki'ah. (Note: there he says that he removed them before Shki'ah!)

Kaf ha'Chayim (30:5): The Ari Zal was very careful to remove Tefilin before Shki'ah.

Mishnah Berurah (8): Ein Morin Ken, lest others put them on l'Chatchilah (at night). Therefore, on a fast day one should not pray Ma'ariv with Tefilin on while it is still day.