2018 H4 extension, how long? 3 months?

2016 , OPT expires, transfer to H4  and apply for EAD , concurrent, wait about 3 months

now H1b already extend for 1 yr, H4 need to do extension seperately, how long does it take? 3 months?

so I can not edit my post? well...just asked lawyer, said h4 extension and ead extension should be file differently, I could extend H4 now as it may take long, while H4 ead can only be extended 6 months before expire...