According to wikipedia article on <a href="https://en.wikipedia.org/wiki/Yitang_Zhang">Yitang Zhang</a>, he had a long pause from 1991 to 1999, after obtaining his phd. During this period he had multiple jobs outside academia. In 1999, he obtained a position as a lecturer at the University of New Hampshire, with only one publication in 2001 until his important work on bounded gaps between primes, published in 2014 in Annals of mathematics.