There is no minimum amount of time you are required to work for your current employer before changing to a different employer. If you find a great new job just a few days after you change status to H-1B, and the employer is willing to file the change-of-employer (or “transfer”, or “portability”) petition on your behalf, you can take it! 

(Of course, aside from H-1B or other U.S. immigration considerations, it may not be a good idea to switch jobs frequently, especially if you are in an industry where the companies are hiring from a small pool of applicants, but that’s not a legal question, more like a career question!)

You can begin working for your new employer as soon as you have proof that your new employer’s H-1B petition has been received by the USCIS. 

The receipt notice, Form I-797C, usually comes to the employer about a week to ten days after the petition has been submitted, but you don’t have to wait for that notice to begin working for your new employer. Once you have proof that the petition was delivered – by UPS, USPS, or FedEx – you can go to work for the new employer. 

For example, if your petition is submitted on Monday, May 1, and arrives at the USCIS on Tuesday, May 2, you are allowed to start work for your new employer on Wednesday, May 3. 

Many foreign nationals prefer not to switch employers until the receipt notice has arrived, and they also don’t want to take any time off between employers, so that they don’t have any time that they are in the U.S. in H-1B status when they weren’t actually working for a U.S. employer. In that case, you would give your employer your two-weeks’ notice on May 3 and then begin working for your new employer on Wednesday, May 17.

If your petition is filed without Premium Processing, it may take months to be approved, but again, you don’t need to wait for that approval to switch employers. However, if you file with Premium Processing, the USCIS must return a decision on the petition within 15 days from receipt. This could mean that USCIS approved the change of employer, but you worked for another day or two for your previous employer. This might make you nervous about violating immigration regulations, but it usually doesn’t cause any trouble. On the other hand, there may be problems if you are not working in the U.S. as required by the H-1B regulations for a substantial period of time.

There is no guaranteed “grace period” for H-1B workers, but you may be granted a discretionary 10-day grace period beyond the expiration of your Form I-797A. You may see that the end date on your I-94 at the bottom of your approval notice is later than the end date of the approval notice itself. The maximum grace period that the USCIS may grant is 60 days or the end date on your approval notice, whichever is shorter. But again, this is at the pleasure (“discretion”) of the USCIS. Most foreign nationals in H-1B status prefer not to take chances with it.