A valid H1B visa holder can transfer to another job as long as he or she is in lawful status and has not engaged in any unauthorized employment. The process for an H1B transfer is the same as the process for filing a new H1B petition, and, therefore, can take the same amount of time. However, you need not wait until your H1B transfer petition has been approved before you start working for the new employer. Rather, you can start working for the new employer as soon as your H1B transfer petition has been filed. Generally, to be safe, it is advised waiting until you receive the USCIS receipt notice for the H1B transfer petition before beginning the new employment. If you would like to know whether your H1B has been approved before starting your new employment, USCIS offers the Premium Processing Service for an additional fee, in which it will process the H1B petition within 15 days of receipt.