Despite living here in Miami, I cannot tell you personally what the lounge offers. However, this AA
webpage has all the information you need about their Admiral clubs at MIA
. There is a closing time (11:30) but for the complete information I'll direct you here.
I'd also like to mention that MIA
is the last place I would want to spend the night...well terminals A and H are nice but I'm guessing you are not departing from there (unless US Express leaves from H too)...have fun though spotting! Search for some other posts about 'what to do at MIA
'....find a nice airport-side place to eat and spot!