Visa requirement for US citizen wants to visit Shenzhen for one day business meeting from Hong Kong

I am visiting Hong Kong and wish to meet for a one day business meeting in Shenzhen. I understand as a US national I am not eligible for a VOA. Would I be able to get a short term one in Hong Kong without waiting period? I only have two days lead time from arrival in HK to proposed meeting in Shenzhen, can I get one on such short notice?
Thank you,
Mark