Offline visual studio's signed account has gone stale copy OnlineLicensing folder to offline computer's location C:\Users\username\AppData\Local\Microsoft\VSCommon

your licence has gone stale and must be updated

 

Copy from 

https://stackoverflow.com/questions/43390466/is-visual-studio-community-a-30-day-trial.

 

To bypass "30days left must go online to sign-in", sign-in once to Microsoft account, you'll get %LocalAppData%\Microsoft\VSCommon\OnlineLicensing folder that you can copy to offline PC's matched location,such as C:\Users\username\AppData\Local\Microsoft\VSCommon