Adjustment of Status - I-485

Hi! I was looking everywhere and can not find anyone who has case like mine: I am a daughter of US citizen older than 21. (F1) and I am here in US legally, attending a college almost for 7 years :)

Here is my mainframe:
priority date Jun 24, 2009,
approval Jul 27, 2011,
AOS process started Jan 19, 2016,
bio-metric appointment Feb 12, 2016
Work Authorization card received on April 23, 2016

Now it is on this point:
"On March 31, 2016, we received your response to our Request for Evidence for your Form I-485, Application to Register Permanent Residence or to Adjust Status, Receipt Number MSC YYYY . Our National Benefits Center office will begin working on your case again. We will mail you a decision or notify you if we need something from you."

I wonder how long to wait in my case? Also I am full time student,(International student on form I-20 status extended) but since my case is pending, how is safe for me to drop my student status? Because I have to pay very high rate tuition and it is very hard.
If someone also student like me making AOS based on family immigration (not marriage!) please share your experience!
Thank you!!