This article is from the FAQ, by with numerous contributions by others.
It is permissible to hold many H-1's separately as long as the total
period does not exceed six years. For instance, if you held one
part time and one full time H-1 from 1/1/96-12/31/96, you have only
spent ONE year on H-1. This is so even though you held two H-1 jobs
simultaneously during this time. The jobs may be both part time or
one full and one part time. The number of hours worked is irrelevant
for this determination.