If this review time period caused Hey to miss their launch date, this is a major signal that their developers do not have ANY experience with the iOS App Store.
> That is because users are required to login with an existing account to use the functionality.
Again, this is clearly spelled out in the Apple App Store requirements. You MUST provide credential for reviews, and those credentials must work. Additionaly, if you are pushing users to login through an external provider, providing a "Demo Mode" is an easy way around App Store restrictions.
This entire article reaks of inexperience, which is pretty incredible since Hey has gone through similar in the past[0].
My suggestion, hire software engineers with experience releasing to the app store.