Question about shift differentials!

Hello! I was just hired as a new grad lvn in med-surg at a really good hospital. However the pay is 16.72 and hour , which is fine but I'm working nocs here!!!

Hr tells me that my differential is 4.50$ for the whole night! Does that mean that I'm only getting an extra 4.50$ for 12 hours or extra 4.50$ EVery hour? (both don't seem to make sense, an extra 4.50 a NIGHT is ludacris where as an extra 4.50 per hour seems like a lot)

confused! =)