First of all, an H-1B employee CAN be part time. There are no minimum hours defined by the regulations and, in the past, our office has prepared H petitions for nurses working one three hour shift on a Saturday. In fact, we have had many health care professionals over the years who have had three or four concurrent petitions, with all jobs being part time. In these cases, INS seems to use a "common sense" approach and, for the most part, is pretty fair about it. The unwritten rationale we have seen is basically "if they are working enough hours for us to believe that they can financially support themselves, then we'll approve it." I have had H-1Bs which have worked ONE part time job, with as little as 20 hours. They just want to make sure that your H-1B employment is enough so that they won't run into you at the Drive Thru asking "Would you like fries with that?"...

For permanent offers leading to permanent residency, the standards do require full time employment and part time is not enough. The definition of full time, however, is all over the place, depending on who you ask:

1. The generally accepted period is 35 hours a week. The reason most knowledgeable immigration attorneys cite this is because it is really the only specific period appearing in the language of the Immigration law. Specifically, this appears in the statutory provisions about the EB-5 Immigrant Investor visa, and it relates to how such investors must establish 10 full time positions, defined as at least 35 hours per week. So, it SEEMS to make sense that this definition would apply across the board, right? Well, I'm not sure...read on...
2. In the legislation relating to Registered Nurses, full time is defined as "40 hours or more."
3. The Department of Labor (which disagrees on many issues with the INS) says that "full time" is "40 hours," or whatever is "normal" for that particular industry or position. Let's say, for example, that air traffic controllers work 30 hours a week because of the stress. Then, in that case 30 hours would be "full time."
4. Finally, according to my CPA, the IRS has a whole set of other angles on what is full time, what is part time, and what is independent contracting. (BY THE WAY: The INS requires an employer/employee relationship with all employment based categories. This is why being an independent contractor and getting paid with a 1099 instead of a W-2 won't fly for immigration purposes.)

As you see, the answer is less than clear. Unfortunately, due to the reality of the workload, this level of analysis is rarely undertaken when INS is adjudicating a case. My recommendation is that the most conservative approach would be to try to meet the 35 hours, which can at least be justified by the EB-5 definition of full time employment.