You can apply with in your last 90 days of your EAD time,
It is good and easy to apply online. after apply on line you need to send the copy by mail, As part of it after filling you have to Call USCIS and schedule an appointment to local INS office for digital photo and finger prints.
you can see a Lud aftet you take digital photo and finger prints.
in 60 to 90 days you will get it.
It is simple very very easy.
before go online get the paper form print out and fill it manually It helps a lot. you can create an accout(login) and fill forms. if youhave a doubt, you can save it and go back again to complete and submit later.