Please remember, there is NO legimate term of "H1b transfer". If you change a job, your new employer must apply for a new H1b for you. The reason why people still use this term is that it is quite flexible for H1b changing jobs, for example for a H1b working for a non-profit employer changing to a new H1b for another non-profit employer, or a H1b working for a profit employer to another profit employer, the applicant can start to working when he/she receives application receipt from INS from the date proposed in the new application. But for changing from a non-profit to profit employer, if no quota is available, there is no way that the new employer can apply for a new H1b for you, of course the question of "when can I start to work" is meaningless.