回复:关于转身份的时间问题.十万火急!
strictly, you must file I539 within 10 days after 4-12.
But practically, if you can produce last pay stub that is reasonably close to the received date of new application (I129, 539 or whatever), your COS has a good chance of approval. The proof of COS approval will be a new I-94 in the bottom right of I-797.