When can H1B extension be filed?

[DTW_Auto]

Hello,

My most recent I-797 and I-94 expires on 10/31/2017. I have an I-140 approved (priority date March 14, 2014). When can my employer start the H1-B extension process? I have heard that H1-B extension can only be filed 6 months prior to I-94/H1 expiry. So the earliest my employer can start the extension would be May 01. Is this correct?

[rohang]

yes