My preference is to be able to give my current employer 2 weeks notice. This will allow them time to find someone to take over my position. If the interviewer really wants you in the next 2 weeks, they will offer you the job. You will be able to give your 2 weeks at your current job, and the interviewer knows that you are loyal, even when leaving. They will understand that you will not leave without giving them 2 weeks notice, and it implies you are someone that can be counted on to do the right thing.