What is the exact expiry date of ur OPT? If your OPT's expiry date is any day after the February first week, then you can stay legally in US if your company files for H1 in April 1. In other words, if April 1st or 2nd (usual H1 application days) falls on the 60 days grace period after the OPT expiry and if your employer files for H1 in usual H1 application period within the grace period, you can stay in US. But you are not allowed to work till next October since ur opt is already expired before applying H1.  You can stay in US and are allowed to work from OCtober only if ur H1 is approved.