Should one only wear a Tallit during the daily main prayers three times a day or can one wear a Tallit whenever they pray to G-d.
A tallis gadol is worn every morning at shacharis (morning prayer), the only time you'd wear a tallis gadol at night would be Yom Kipur eve.
Tallis katon is worn all day every day, independent of prayer. Some people would wear it at night as well but im unsure whether they believe its halacha or just a chumra.
A regular (vs. Shaliach Tzibur) only wears a Tallis Gadol at shachris. For Ashkenazi, only on Tisha Beav isnit worn by Mincha. Some Sefardic Communities follow the ruling to wear it (alongside Tefillin) on every fast day.
This is the Minhag, but halachically one can wear it all day long except for Maariv and afterwards, even if it is still before night fall with the exception of Yom Kippur- see Rema O"C 18:1, Mishna Berura 18:4
The Mishna Berura adds that a shaliach Tzibur is exempt from this and can wear a tallis even for the Maariv. This is because a Shaliach Tzibur only wears the Tallis for the dignity of the congregation and not in order to fulfill the Mitzva of Tzitzis. Note that the customs vary across communities as to the wearing of a Tallis by the Shaliach Tzibur for every tefillah, some only do so by Shachris.