Time allowed between when three month visa-on-arrival application has been paid for and approved. and the actual arrival in Vietnam is at least 50 days later.

We applied on line for a three month visa-on-arrival beginning on May 24 and paid fees. We received the approval forms at that time. On the day before leaving the US my wife broke her arm and we had to delay our departure until July 10, approximately, because the surgeon advised against air travel while her arm is in a cast. Can we still use that same approval form when we arrive in Saigon on approximately July 12? If the application form that we have is valid to be used on our July entry, will we be able to stay the full three months in Vietnam after our arrival in July?