I have not raised any SR yet.
If H4 EAD is filed with H1/H4 then they get approved together. If H4 EAD is filed separately and that too with H4 receipt, then it takes time. They start considering H4 EAD application after H4 is approved. So it will take 2-3 months from H4 approval date. You can say this H4 EAD application is received on Jan 30, 2018 (date when H4 was approved).
One of my friend did the same last year. When H4 was approved, he called USCIS. They said your application real time starts now after H4 approval. It was approved 2 months later.
Moreover this is with Vermont center (slowest in all). Vermont is processing September I-765 applications.