Mishna Berura 18:4 says that on a fast day where we wear a Talis for Mincha you should take it off before Barchu of Maariv since Laila Lav Zeman Tzitzis. However he says a Shaliach Tzubur may continue to wear it if without it he would be inappropriately dressed.
Having Davened in both Nusach Ashkenaz and Nusach Sefard Shuls I have seen that by Nusach Ashkenaz they do not wear the Talis over the head by Maariv. (for instance Friday night, Motzei Yom Kippur, etc.). However by Nusach Sefard they do wear the Talis over the head by Maariv (Friday night, Motzei Yom Kippur, etc.). Perhaps the reason Nusach Ashkenaz does not put the Talis over the head in the evening has to do with ("לילה לאו זמן ציצית") the evening is not the time for Tzitzis, and therefore to indicate that they do not put it over their head. Piskei Teshuvos 18 says that Nusach Sefard holds that on Shabbos and on Motzei Yom Kippur that you may wear the Talis over the head. On Shabbos since the light of Shabbos allows it and on Motzei Yom Kippur since we are like angels.