The code-signing needs to happen through a trusted / certified timestamp server, it's not using the local timestamp. This process basically guarantees that the application used a valid certificate at the time it was signed, and that it wasn't tampered with since then.
With this, the time when code-signed application is executed doesn't matter at all, fake date or not.
With this, the time when code-signed application is executed doesn't matter at all, fake date or not.