I have been in a trading environment and don't think people in sales and trading on Wall Street work that much on the weekends or late into the night -- the markets are closed. Someone who is gifted in math and interested in being a trader should understand that the cultures in investment banking and trading differ.
Finance is a huge field. The hours vary as much as it does in medicine. In both industries there are a small fraction of people that work crazy hours, and many more that work 9-5 style jobs. Many traders basically work the hours the US market is open: They get in about 9AM and leave as soon as they can after 4PM. My current field, money management, has relaxed hours as well. My typical work day is anywhere from 7 - 9 hours.
