H1B Extension filed on 1 day before I94 expiry date. when should I apply for change of status from H1 to H4 to avoid out of status?

If your I-94 expiration date was March 12 and your employer applied for your eighth year extension on March 9 and the H-1B petition was properly receipted by the expiration date, the extension petition would be legal as long as the I-140 or labor certification application has been pending 365 days. In point of fact, most immigration practitioners including me would argue that you have a 10 day grace period from the ending of your H-1B status in which the petition extension could be filed. I do not quite understand the concern unless there are other factors in your H-1B extension petition which have not been explained.Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.