Uh, what?
Why should I, as a customer of a hosted, managed, SaaS product, need to ever care or think about the time of day as a factor for the performance of my product? If Fastly, as a hosted SaaS, isn't managing its own capacity well enough to deliver consistent performance at all times, that's on them.
Additionally, provisioning hidden limits between different types of accounts, especially limits that affect performance for a CDN whose objective should be delivering consistent performance, is deceptive at best, and malicious and false advertising at worst.