What's a nice, quiet coffee shop that opens late around Union Square SF?

I don’t know the San Francisco area very well but here are a few places in that area with good reviews from locals. Follow the links for more info and to review customer comments for yourself. I hope this helps!

Jasmin’s Cafe is on 809 Bush Street and open til 10pm.
http://www.yelp.com/biz/jasmins-cafe-san-francisco

The Coffee Bean and Tea Leaf is on 773 Market St and also open til 10pm.
http://www.yelp.com/biz/the-coffee-bean-and-tea-leaf-san-francisco-2

Latte Express is on 48 5th St and open 24 hours! Looks like they serve lots of other foods so it will probably have a bit less of a coffee/book place atmosphere and more of a restaurant feeling. However, they will be open no matter what time you get off work.
http://www.yelp.com/biz/latte-express-san-francisco-4

I found these listings and many more like them Yelp. You can access and explore more listings for places to get a coffee, as well as customer reviews of these places here:
http://www.yelp.com/search?cflt=coffee&find_loc=Union+Square%2C+San+Francisco%2C+CA#bbox=-122.413830757%2C37.7816032884%2C-122.400870323%2C37.7918458804

Here is a tinyurl, in case the longer link above gets broken:
http://tinyurl.com/yhcf524

I hope you find a good place to go after work. Good Luck!