case approved but when to go for stamping??

hello everyone,

i applied for H1b for FY2017 on 1st april 2016. after the RFE status for a long time, my case is approved on 8th march. but due to some family problem i can to go USA in second week of May 2017.

now i want to know when should i go for stamping?

plz give your valuable opinion.