Sooner. I'm pretty sure this is standard technique among bamboo cultivators trying to get a few fat culms. No point letting it waste its energy on culms you don't want. I think some people even think that one should reduce the number of shoots anyway to get it to concentrate its energy on a smaller number of fat shoots. I find that some bamboos have a large number of culms that abort, and part of the problem is too many shoots starting for the energy available.